Heinrich J.G., Aldinger F. (Eds.) Ceramic Materials and Components for Engines

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MODEL-DUST

'CaO

26.70

lCaO

14.68

A1203

14.00

IA1203

0.20

Fig.

SEM-micrograph of the nano-scaled filter mem-

brane (Apau.

700

Pa,

1200 "C, ts

h).

ZnO

2.42

Po3

2.36

The sintering behaviour of the produced membranes

reflects a low sintering activity in the investigated tem-

perature range, in spite of their small particle size. Thus

may

related to the

and GA1203-powder used.

general, sintering of

and 6A1203 is characterized by a

phase transformation of the unstable

and 6-A1203 into

the stable a-A1203, followed by an accelerated sintering

neck formation and grain coarsening

[3].

The phase

transformation is shifted to lower temperatures with

increasing densification of the powder. Investigations

concerning the sintering behaviour and the phase trans-

formation of

and 6A1203

[4]

revealed, that phase

transformation in powders required a temperature of

1300 "C, whilst in compacted bodies a complete trans-

formation was already achieved at 1055 "C. Investiga-

tions of the author to the sintering behaviour of loose

powder exhibited significant sintering neck formation

and grain coarsening at sintering temperatures of

1200 "C for a dwell time of minimum 1 hour. However,

the agglomerates of the loose powder were denser than

the produced membrane.

So,

due to the structure of the

membrane (high porosity, few contact points) phase

transformation and subsequently sintering is hindered in

the limited temperature range.

the one hand, this

behaviour is favourable in that it results

a minimal

additional pressure drop increase of the sintered mem-

branes and in a minimal grain coarsening. But

the

other hand, the obtained structure also leads to a low

mechanical stability of the membranes. For all chosen

sintering parameters the produced nano-scaled mem-

branes could be damaged mechanically.

Nevertheless, filtration and recleaning tests turned

out, that the stability of the sintered membranes over-

comes the appearing flow forces, more than sufficient

for the relevant operating range. Therefore, it was de-

cided to continue the filter performance tests with mem-

branes sintered at

1200 "C for a dwell time of

hours.

Further optimisation relating to the mechanical

stability is part of actual work.

ZnO

0-11.94

thermal waste treatment processes, e.g. combus-

tion, gasification or pyrolysis of bio mass and waste, the

high number of input substances and possible inter-

actions results in a wide variety of compounds in the

fly

ashes.

general, these particulates are characterized by

a high amount of hazardous components. Moreover,

they exhibit low softening temperatures, a high fraction

of fine particles and

in combination with the flue

gases

a high corrosion potential. The strongly fluctu-

ating and heterogeneous waste composition additionally

causes these properties to vary considerably.

In order to exclude unknown toxic effects and to fa-

cilitate handling, a model dust was developed for the

simulation of dusts from thermal waste treatment proc-

esses. Its composition is based on investigations of

fly

ashes and dusts from waste incineration plants

[5-81.

For real dusts, the airborne particle characteristics play a

significant role in filter cake formation. The morphol-

ogy of these particles

can

classified in

[5,6]:

Fused

Spheres

(Spheroids of various colours)

Crystals

(irregular shaped particles similar to calcite)

Polycrystullines

(Dense agglomerates)

Opuques

(Single, large irregular shaped particles)

Char

(unburned, black fibrous particles)

By mass, more than the half consists of large ir-

regular shaped particles, which exists as single particles

or as agglomerates. Critical to the hot gas filtration with

ceramic filters are the micronhubmicron size particu-

lates, mainly fUsed spheres and crystals. This fraction

dominates the fiequency distribution with

whereas the mass is almost negligible. The better the

operation of the incinerator the more the total particle

size distribution will shift to smaller particle sizes and

filter clogging due to the fine dust content becomes

more stringent. The total dust loading in waste incinera-

tion ranges typically from 2 to 10 am3

[8,9]

Table

Typical components of the fly ash from waste

incinerators in comparison to the model-dust.

SO3

7.25

IS03

13.95

0.10

Fed-

5.20

IFeO*

3.72

IkO

10.05-11.56

2.51

lCl

9.51

10.41

Cr203

0.64

others

7.10

INa20

6.85

lMg0

1.65

As for the model-dust a composition of

wt.-%

soda-lime glass spheres (A-glass), 30

wt.-%

columnar

gypsum (CaSO,

2H20), and

wt.-%

KCI

ZnCI2

particles was chosen.

Table

this composition is

compared to those of typical fly ash fiom waste incin-

erators.

promote the pollutant-forming and corrosive

properties, the sulphate and chloride

fractions

in the

model dust were increased. The chloride mixture also

served to

set

various softening temperatures. Thermal

properties of single and mixed dust components

are

shown in

Table

16000

150OO

14000

13000

12000

11000-

10000

-I

Table

Selected thermal properties of single salts,

binary eutectic mixtures

[

101 and of A-glass.

100

kPa

14001

432

(mix.C\

Softening Point

A-Glass

600

Fig.

SEM-micrograph of model-dust mixture A

(50

wt.-%

A-glass

wt.-%

Gypsum

13.64

wt.-%

ZnCl2

6.36

wt.-%

KCI).

0.1 1 10 100

Diameter,

Fig.

Particle size distribution of model-dust mixture

A, measured by laser scattering spectrometry (mean

6.3 pm, std. dev. 5.2 pm).

The typical morphology

the model dust is re-

flected

figure

The mixture exhibited a bimodal

particle size distribution with maxima at about

500

and 10

(Fig.

7).

Typical mean particle size was

about 6.3

at maximum values up to

pm.

Hence, by using

wt.-%

soda-lime glass spheres,

wt.-%

columnar

gypsum,

and

wt.-%

KCI or ZnC12

particles, not only a relevant particle size of

30 pm

could

set,

but also the particle shape and dust compo-

sition of real dusts could

approximated. Furthermore,

this model dust allows to simulate the softening behav-

iour of real dusts in a wide temperature range. For

in-

vestigating the operating behaviour of filter media, the

critical temperature ranges

can

varied fiom about

230 "C up to about 800 "C

under exclusion of ZnCl?.

FILTRATION

PERFORMANCE

assign the filtration performance of the nano-

scaled filter membranes at conditions, relevant to hot

gas filtration, filtration and recleaning tests were per-

formed at a temperature of

780°C. Based on the

thermal properties of the model-dust components (table

3) at this temperature, the A-glass will be softened

whilst the

KCI

is molten and the ZnC12 is evaporated.

Therefore, a model-dust mixture of

wt.-%

A-glass,

wt.-%

gypsum and 20

wt.-%

KCI (mixture

has to

be used in these tests. The investigations were carried

out at the experimental device represented in figure 1, at

a filtration velocity of uF

cm/s. Here, the dust was

fed via

the

brush type dust feeder into the filter section.

Recleaning was performed pressure drop controlled at a

loading pressure up to pL

130 kPa.

Fig.

Operating performance of the Nano-3-2SPK

ceramic

filtration

and

recleaning of model-dust

mixture

(50wt.-%

A-glass

wt.-%

Gypsum

wt.-%

KCl) at TF

780 "C and

c~/s.

Figure

reflects the performance of the Nano-3-

2SPK ceramic with respect to regeneration. The cycles

are characterised by the formation of a dust layer until

the maximum pressure drop for recleaning was reached.

Subsequent, the differential pressure dropped down by

the

fast pressure decrease of the recleaning method

applied and the formation of a new dust layer started.

Recleaning intensity of the formed filter cake could be

enhanced by an increase of the loading pressure fiom

100 to 130 kPa. At pL

130 kPa, the residual pressure

drop was in the range of the initial pressure drop,

corre-

sponding to an almost complete detachment of the filter

cake. Hence, with the produced nano-scaled ceramic

filter membrane and the recleaning method applied,

detachment of fine and sticky dust

was

enabled within

the observed cycles, even at the

chosen

extreme condi-

tions. These tests are continued with respect to long

term

stable operating behaviour.

CONCLUSIONS

In high temperature dust separation using ceramic

filter media, the filtration and recleaning of fine and

sticky dusts is a major problem. For conventional filters,

these dusts often lead to an enhanced filter clogging and

long-term stable operation is limited. To overcome

this

problem, a standard filter ceramic

was

coated by the

filtration of A1203-nanoparticles with a mean grain size

of 78

nm.

Optimum membranes were achieved for an

additional pressure drop of about 700

Pa.

After sinter-

ing, the membranes exhibited a porosity of 80 to 90

with pore channel diameters up to 2

pm.

Membrane

thickness was in a range

between

2 and 7 pm. However,

due to the limited sintering temperature of 1300"C,

sintering

the membranes was hindered. Although the

stability

the membranes overcomes the appearing

flow forces, they could be damaged mechanically. Thus

will

solved, among others, by optimization of the

multilayer structure and by the

use

of supporting mate-

rials which allow higher sintering temperatures.

Filtration and recleaning tests performed with a he

and sticky model-dust showed an excellent filtration and

recleaning behaviour

the produced nano-scaled

ce-

ramic membranes, even at a temperature

780°C.

Therefore, a great potential for the separation of critical

dusts is offered by those membranes, not only in ther-

mal waste treatment processes but also in product re-

covery. The beneficial properties of the nano-particles

will be further enhanced by using ceramic nano-

particles with smaller grain size distribution and smaller

mean diameter.

For investigating the operating behaviour of filter

media, the critical temperature ranges of real dusts

can

be simulated with a

four

three

component model-dust

fiom about 230

up to 800 "C. Here, especially the

important softening, melting or boiling

local eutectics

can be replicated.

ACKNOWLEDGEMENT

The authors wish to acknowledge the European

Commission DG

XII

for partially sponsoring this work

under the Industrial and Materials Technology

Pro-

gramme (BRITE EURAM

111)

in the BRITE EURAM

Basic Research Project "HOTFIL" BRPR

CT97

0472.

REFERENCES

T. Pilz, Particle Properties relevant for Hot Gas

Cleaning with rigid barrier filters and their Char-

acterization at High Temperatures, in Schmidt et

al.

(eds.):

High Temperature

Gas

Cleaning, Institut

f3r

Mechanische Verhhrenstechnik und Mechanik

der Universitiit Karlsruhe (TH), Karlsruhe,

(

1996),

I.V. Beketov et al., Synthesis of Nanometer-Sized

Powders of Alumina and Titania Using the Elec-

trical Explosion of Wires. Roc. Fourth Euro Ce-

ramics Vol. 1, (1995), 77-82

A. Weisenburger, Anwendung der Hochleistungs-

impuls- und Mikrowellentechnik

zur

Herstellung

nanokristalliner pulver und Festkiirper. Dissertati-

on Universim Karlsruhe, (1 999)

V.Ivanov, V. Khrustov,

Proc.

Fourth Euro Ce-

ramics Vol. 2, (1995), 281-288

A.J. Chandler et al., Municipal solid waste incin-

erator residues. Elsevier Studies in Environmental

Science 67, Elsevier, 1997, ISBN 0-444-82563-0

Waste Programme, Waste Analysis, Sampling,

Testing and Evaluation Program, Phase 1 Final

Draft Report Prepared for Environment Canada,

US EPA and the International Lead Zinc Research

Organisation, unpublished 1993

N.F. Glen and J.H. Hod, Modelling Refhe

Incineration Fouling, Publication C 1 18/88 Na-

tional Engineering Laboratory, Glasgow 1988

P.J. Hayes,

Schulz, H. Leibold, B. Zimmerlin,

B. O'Reilly and P.

Hahn,

Hot gas cleaning using

advanced ceramic filter technology for municipal

waste incinerators (HOTFIL)

Review of ash and

gas compositions, TRAWMAR Workshop Pro-

ceedings Sept. 1998, Rhodes

P.J. Hayes, H. Leibold, B. Zimmerlin, R. Schulz,

A. Zagorski and

Hahn,

Hot gas cleaning using

advanced ceramic filter technology for municipal

waste incinerators (HOTFIL)

Synthetic dust for

modelling high temperature filter cake behaviour

in MSW incinerators, TRAWMAR Workshop

Proceedings Sept. 1999, San Sebastian

132- 143

(10) G.J. Janz, Molten Salts Handbook, Academic

Press,

1967

PRODUCTION AND CHARACTERIZATION OF TiCN-BASED

MATERIALS FOR CUTTING TOOL APPLICATIONS

F. Monteverde*,

Bellosi*, C. Zancolij**, M.

Faga**

(*)

CNR-IRTEC, Istituto di Ricerche Tecnologiche per la Cerarnica,

48018

Faenza

(RA),

Italy

(**)

CNR-ILM, Istituto Lavorazione Metalli, 10043 Orbassano

(TO),

Italy

ABSTRACT

Nearly full dense Ti(C,N)-based materials were

obtained by hot pressing and gas pressure sintering.

The starting compositions were based on mixtures of

TiCo.5No.5 and WC(S%Co) powders with moderate

content of metal additives (6.2wt% Ni, 2.lwt% Co) or

additive fiee. Microstructure and mechanical

properties were studied and related to starting

composition and processing conditions. Cutting tools

were obtained fiom the sintered materials and

preliminary results on metal machining tests were

reported.

INTRODUCTION

Titanium carbonitrides are very hard materials with

increasing technical importance. They are mainly

applied in composites with various metal carbides

and/or binders (cermets) for metal cutting operations

[I-41. Cermets can be described as composites

ceramic particles (carbides, borides, nitrides or a

combination of them) bonded together with a metal-

based system (i.e Fey Ni Co, Mo or an alloy

of them)

[l-3, 5-71. The notable hardness and wear resistance

are provided by the hard particles, while the binder

phase improves the ductility and yields better

toughness and thermal shock resistance. For many

applications, included metal cutting tools, the ideal

material should exhibit the highest hardness as well

the best toughness. However, as hardness and

toughness are generally antagonist properties, a

compromise has to be set or, keeping in mind the

specific application of the component, to favour one of

them. Titanium carbonitrides based cermets are

characterized by high creep and difhsion wear

resistance, due to the formation during sintering of the

well

known core-rim type structure

[l].

The

microstructure of TiCN-based cermets ranges fiom

usual ceramic configuration with low content of

metallic phases (i.e binder) at grain boundaries, to

metal-ceramic composites where alloys constitute a

frame with ceramic particles dispersed inside.

Moreover, the composition of the binder is dependent

on the overall stoichiometry and nitrogedcarbon

content of the hard constituents [l, 8-10]. The physical

and mechanical properties of these cermets can be

adjusted within certain limits to meet the requirements

of the application through the selection

of the raw

powders, the design of the compositions and the tuning

of the processing parameters. Concerning these hard

metallic systems, the occurrence of liquid phase during

sintering, the mutual solubilities between these

complex carbideslnitrides and the binder are key

factors that may bring effective benefits improving the

expected performances [5-171.

this

work TiCN-WC(Co)-based materials (with

moderate addition of Ni-Co or additive fiee) were hot

pressed

(HP) and gas pressure sintered (GPS).

Microstructure and some structural properties are

described and discussed. Preliminary results of metal

machining tests, in finishing operation using the

additive fiee material as cutting tool, are reported.

EXPERIMENTAL PROCEDURES

The commercial raw powders used in this work are

listed as follows: Ti(C,N) (HCST

50/50

grade E,

Germany), WC-S%Co (Nanocarb, Nanodyne

USA),

Ni (Carbonyle), Co (Sherrit). The Ti(C,N) powder has

a stoichiometry TiCo.sNo.5 and mean particle size 0.36

The following two mixtures (amounts in

wt%)

mixture

TiCo.5No.5

16.7 (WC-5Co)

mixture

TiCo.5No.5

15.3(WC-5Co)+6.2 Ni+2.lCo

were prepared. Sintering of mixture A and

B was

accomplished through low vacuum hot pressing

(HP)

and gas pressure sintering (GPS). The thermal cycles

were scheduled as follows:

HP1: 20"C/min to 1700"C, 1700°C for 30 min 30 MPa;

HP2: 20"C/min to 1650"C, 1650°C for 45 min,

MPa;

GPS: 10"C/min up to 1650°C and 1650°C for 30

minutes in flowing gas (0.1

ma); raising the gas

pressure up to 2 MPa and holding it for 30 minutes.

The microstructural characteristics were analyzed

on the dense materials by XRD and SEM/EDX.

Several mechanical properties were investigated using

the following methods: -Young's modulus

(E):

resonance fie uency method on plate

(28.0x8.0x0.8)mm

;

-Vicker's microhardness (HV1

.O)

with a load of 1Kg;

4-pt flexural strength

(0)

on bars

(25.0~2.0~2.50)

mm3

up to 1000°C; -fracture

toughness

(Klc)

by the direct crack measurement

method (load 10Kg) on polished surfaces using the

models proposed by Anstis et al.

[

181 and by Evans et

al. [19].

The cutting performance

inserts obtained fiom

the material

HPA

were tested

longitudinal turning

tests in comparison with a similar commercial tool.

Continuous cutting tests were carried out according to

the

IS0

3685 standard for the part concerning tool

wear criteria. During machining tests the flank wear

evolution was monitored using an optical microscope.

SEM analyses were performed on the cutting tool

after

the tests.

Sample

HPA

HPB

GPSB1

RESULTS

AND

DISCUSSION

Thermal Atmosphere Density Mean Crystalline

cycle Grain size phases

HP1 Vacuum

5.75

100

0.55

(Ti,W)(C,N), TKN)

HP2 Vacuum 5.82 98

0.75

(Ti,WC,N), Ti(C,N)

binder (a=0.354

nm)

GPS N2 5.92 99.8

0.6

(Ti,W)(C,N), Ti(C,N)

gr/cm3

Cun

Microstructure

GPSB2

The microstructure of the dense additive fiee

sample HPA shows the typical core-rim structure; the

Z-constrast imaging mode allows to distinguish the

inner core Ti(C,N) fiom the outer rim (Ti,W)(C,N)

(Fig. le). Ti(C,N) can be drawn as a solid solution

between the boundary phases TIC and TiN,

(Ti,W)(C,N) is a solid solution

well containing W

ions. These two phases are isomorphous with fairly

close cell parameter

[7,

161.

From the spectra obtained by windowless energy

dispersive microanalysis, only part of the original

TiCo.sNo.5 grains constitute the inner core that in

turn

contains the main percentage of the nitrogen fiom the

starting mixture.

Any

trace of W was found in the inner

cores. On the other hand WC undewent complete

dissolution during the heat treatment, and cubic

(Ti,W)(C,N) phase precipitated as a

rim

around

Ti(C,N) nuclei. Although the sample was hot pressed,

some microporosity remained (Fig. la) and

this

could

be ascribed to the nitrogen in the formulation partially

released in the temperature range 1200-1300OC [l].

Grain boundaries appear clean with no evidence

intergranular phases.

Dense cermets, HPB

GPSB1

GPSB2, sintered

through a Ni-Co based liquid phase, featured

faceted

grains of hard phases embedded in a binder matrix. The

microstructure

of the as-sintered materials is compared

in Figs lb-d (fkacture surfaces) and lf-h (polished

surfaces). The grains of the hard phase show the typical

core-rim microstructure already observed for material

HPA.

The solubility of TiN in liquid metals is much

lower than that of Tic and WC. Therefore when at

suitable temperature mixtures of TiCN and WC react

with liquid metals, Tic is preferentially dissolved in

comparison to TiN while WC is totally dissolved in the

cubic binder (a=0.355

nm)

cubic binder (a=0.357

nm)

GPS

5.90 99.4 1.2 (TiW)(C,N), Ti(C,N)

liquid phase. Carbon-poor Ti(C,N) residues survive

and act

nuclei for the precipitation of (Ti,W)(C,N)

upon solidification of the liquid phase (Figs. le-h).

The melt resulting immediately after the onset of

the liquid phase

notably rich of W. The inner layer

surrounding the TiN-rich nuclei (Figs. le-h) is hardly

enriched of W than would correspond to the

composition of the powder mixtures [l]. Our

SEMEDX analyses on these selected areas confiied

these features previously reported

[

The sintering conditions and particularly the

nitrogen partial pressure of the atmosphere decisively

influence the phase equilibria, and thus grain growth

and the composition of the sintered phases [l].

Morphology of sample HPB (Fig. lb) and GPSBl (Fig.

lc)

as well as grain size (Table I) are similar. The

binder is well distributed and forms thin layers around

the hard ceramic grains. Concerning the sample

GPSB2 an evident grain

growth took place (Fig. Id)

with the residual binder mainly located in pockets at

the triple points of the hard grains (Fig. 1 h).

Ti(C,N) cores and (Ti,W)(C,N) outer rims, clearly

revealed by SEM-BSED investigations (Fig le-h) are

isomorphous (cubic) phases with fully overlapped

XRD patterns (along the forward angular range).

Semiquantitative calculations of the rim composition in

the three cermets gave the following Tim atomic ratio:

for HPB,

6.5

for GPSB1 and 18 for GPSB2. Since

the total volume of the rims in sample GPSB2 is larger

than that in samples GPSBl and HPB (the amount of

W introduced as WC is the same) the content of W

taken up by the rim shows a reverse relationship with

the rim volume in the materials.

The binder, characterized by a cubic

symmetry,

was

analyzed upon mirror-like flat surfaces

in areas where binder is well localized. The results

indicated that the binder of sample GPSB2 contains 3

times more more W than the cermet GPSB1, in a

reverse relationship with the results aforementioned on

the amount of W in the outer rim. In fact, fiom the

XRD patterns the cell parameter of the binder is higher

for sample GPSB2 (a=

0.357

nm)

due to a higher W

content, than for sample GPSB1 (a=0.355

nm)

and

HPB (a4.354

nm).

Table I. Specifications of the sintering cycles and some microstructural features of the produced materials.

Fig.

SEM

micrographs from fractured (left column, seconury electron mode) and polished (right column, back

scattered electron mode)

material HPA (de). HPB

@If),

GPSB1 (c/g) and GPSB2

(a).

The arrowed

points correspond to:

inner core Ti(C,N), 2+ outer rim (Ti,W)(C,N),

3-+

W-

rich inner rim,

binder.

Table 11.

Grain

size and mechanical properties measured on the dense materials.

(*Anstis et al. model [18], "Evans et al. model [19])

These features appear strongly dependent on the

processing atmosphere. It is well

known

that the grain

growth rate in nitrogen-containing cermets is

much

lower than in nitrogen fiee alloy [1,5], due to

the

fast

achievement of saturation concentration of the liquid

phase with respect to Tic and WC concentration, that a

complete dissolution of the Ti(C,N) particles

never

reached. At suitable temperature (namely >1 600"C),

the solubility of nitrogen is several orders of magnitude

lower than that of carbon and titanium, therefore high

solubility of carbon (into the liquid phase) compared

with that of nitrogen enables a carbon

flux

and thus a

close to uniform carbon activity throughout the sample

[5]. On the contrary, a nitrogen-activity gradient will

result depending on the sintering atmosphere. It

was

reported an enhanced grain growth, due to a high

nitrogen-activity gradient favoured by the argon

atmosphere [5]. The sample GPSB2 in fact has a grain

size double than the sample GPSB1. The atmosphere

condition during hot pressing should favour nitrogen

activity as well, but the presence of

applied pressure

had an effect to limit grain growth.

Mechanical properties

The mechanical properties of

the

dense materials are

reasumed in Table 11. They clearly depend on the

starting compositions and processing conditions.

Hardness: as previously reported [13], it increases with

decreasing grain size

the hard ceramic phase. The

additive fiee sample HPA in fact is the hardest while

cermets fiom mixture B fit the expected behaviour on

the basis of the grain size.

Fracture toughness: the three cermets (fiom mixture B)

resulted tougher than ample

HPA.

The alloy

constituting the binder improves toughness and an

effect

grain size is evident

well. The values

obtained by the formula of Anstis

[

181

are higher than

the values obtained by the formula of Evans and

Charles

[19], but the relative trends result similar.

any case the values estimated fiom the former model

(measured Young's modulus as entry), besides the

crack path length and hardness, can be assumed as

more appropriate.

Young's modulus: the measured values are in

agreement with the ones reported in literature for

similar compositions [l]. The slight variations of the

experimental data could be due to residual porosity and

to specific properties of the binder alloy (only for

cermets).

Flexural strength room and high temperature strength

(Table

II)

of the material HPA is lower

than

that of the

three cermets from mixture

B. (Ti,W)(C,N) phase has

an inherent better wettability with respect to the binder

not only in the liquid but also in the solid state, hence

greatly improving strength

of the cermets [13]. Due to

the difference of the atomic radii, the binder alloy is

strengthened by the

dissolved in it.

Concerning the room temperature strength,

the

influence of fabrication defects and of machining often

mask strengthening effects related to the properties of

the hard phases andor the binders. In any case, the

strongest sample resulted the GPSB2 (i.e gas pressure

sintered in Argon), which contains more

in the

binder phase than the other samples.

High temperature flexural strength in air is affected

not only by the intrinsic microstructural characteristics

but also by new defects induced by extensive oxidation

on surface after hot exposure. The latter represents the

main degradating mechanism of the strength in sample

HPA. As far as the three cermets concern, the tests up

to 800°C fall in the low temperature domain where

similar cermets exhibit brittle behaviour and non

measurable plastic deformation. From

800°C up to

about 1 100°C limited plastic deformation was observed

[15]. Our experiments confii a plastic deformation at

1000°C until fiacture occurs. This behavior may be

ascribed to typical microstructural features (hard phase

grain size, composition

of binder). It was proposed in

fact that the yield stress at constant plastic deformation

is reversely proportional to the square root of the grain

size and that dislocation motion occurs first in the

metallic binder and is associated

with

an anelastic

relaxation process controlled by solute atom diffusion

in the metallic phase

[

151.

Behaviour

metal cutting tools

The potential of the sample HPA as metal cutting tool

in finishing operation was tested following the cutting

parameters and the work materials shown in Table 111.

The results

longitudinal turning tests (Table IV), in

terms of tool life, observed until reaching a flank wear

threshold VB~,,=0.30

mm,

show the better

performance of the HPA insert,

Table 111. Work materials, parameters for cutting tests

Material

Cutting speed Vc,

(dmin)

Feed

(f,

&rev

)

Cutting depth

(ap,

UNI c45 210

UNI

36NiCrMo4 300

UNI

42NiCrMo4V 3 15

250,300,400

0.15,0.20,0.25

0.5,

1.5

Lathe

Type of insert

Toolholder

CNC UTITA

(30

)

SNUN

120408 T

Lubricant

Dimension of the

workpieces

(Chamfered

)

Sandvik Coromat

None

lOOmm,L=450mm

CSRNL 3225P12-1C

under machining conditions of low feed rate and high

cutting speed, due to the specific combination of

mechanical properties of the produced insert. The wear

morphology of the commercial and HPA inserts is

compared in Figs. 2.

Table IV Results of turning tests

(vB~,,,,=0.3

mm)

Work Cutting conditions

Tool life (min)

material f

a,,

HPA

[Corn.

Tests at higher feed and cutting depth evidenced

worse results than commercial materials. Further

experiments under different metal machining

conditions are in progress.

CONCLUSIONS

Different Ti(C,N) based materials were produced

with and without the addition of metallic binders

(Ni,Co).

The influence

starting compositions and of

processing conditions on microstructure and properties

was studied. A core-rim structure resulted: the core is

constituted by partially dissolved raw TiCo,5No.s

powder particles while the rim by (Ti,W)(C,N) solid

solution. Grain size and composition of the rim depend

HPA

insert.

t=4

min.

VBR=0.24

Commercial insert, t

3.41

min,

VBB

0.47

Figure 2. Optical micrographs of the

flank

wear evolution from HF'A (a,b) and commercial (c,d) inserts.

Workpiece material: 36NiCrMo4,

300; cutting conditions: Vc= 400

dmin,

feed=

0.15

mmhev,

depth of cut=

1.5

mm.

mainly on the sintering atmosphere. Gas pressure

sintering under argon favours grain growth, less

amount of W in the rim of the hard grains and more W

in the binder phase, in comparison to cermet gas

pressure sintered under nitrogen or hot pressed in

vacuum.

These features influence mechanical properties. Gas

pressure sintered cermets exhibited the highest strength

in comparison to the hot pressed one. The presence of a

binder effectively strengthened and toughened these

carbonitrides.

Preliminary tests on material

HPA

as metal machining

tool evidenced better performance

than

commercial

inserts under finishing operations at low feed rate and

cutting depth.

As-sintered

1 2

KeV

Fig.

SEM micrograph (upper) fiom the flank of HPA

insert after cutting test. EDX spectrum (lower)

was acquired upon the dark halo and compared

to that of the as-sintered material.

Acknowledgements

This work

was

supported by MURST and

CNR

under

the National Project “Innovative Materials”, Law

‘95.

REFERENCES

(1)

P. Ettmayer, H. Kolaska, W. Lengauer,

Dreyer,

Ti(C,N) Cermets- Metallurgy and Properties,

Int.

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13,

(1995) 343-51.

(2)

Zhang, Material Development of Titanium

Carbonitride-based Cermets for Machinig

Applications,

Key Engineering Materials,

Vol.

138-140,

TTP Switzerland,

(1998) 521-43.

T. Watanabe, T. Dotsu, T. Nakanishi, Sintering

properties and Cutting-Tool Performance

Ti(C,N)-based Ceramics,

Key Engineering

Materials

Vol.

114,

TTP Switzerland,

(1996)

B. Clark, B. Roebuck, Extending the Application

Areas for Titanium Carbonitride Cermets,

Refi.

Met&HardMat.

(1992) 23-33.

P. Gustafson, A. Ostlund, Binder-phase

Enrichment by Dissolution of Cubic Carbides,

Int.

Rep. Met&Hard

Mat.

12 (1 993194) 129-36.

H. Holleck,

Kleykamp, Constitution of

Cemented Carbide Systems,

R&HM,(

1982)112-

16.

T. Laoui, H. Zou,

Van der Biest, Analytical

Electron Microscopy of the CoreRim Structure in

Titanium Carbonitride Cermets,

Int.

of Refi.

Met&Hard Mat.

(1 992) 207- 12.

Ehira,

Egami, Mechanical properties and

Microstructure

of Submicron cermets,

Znt.

Ref?, Met&HardMaf.

(1995) 313-19.

M. Rynemark, Investigation of Equilibria in the

Ti-W-C-N System at

175OoC,

Refi. MefhHard

Mat.

10 (1991) 185-93.

189-266.

(10)

T. Laoui,

Van der Biest, Effect of Tic addition

on the Microstructure and Properties

Ti(C,N)-

WC-Co-Ni Cermet,

Mof.

Sci.

Left.

(1994)

(1 1)

Z. Xingzhong, L. Jiajun, Z. Baoliang, M. Hezhuo,

L. Zhenbi, Wear Mechanisms of Ti(C,N) Ceramic

Sliding Contact with Stainless Steel,

Mat.

Sci.

32 (1997) 2963-68.

(12)

Bolognini, G. Feusier, D. Mari, T. Viatte, W.

Benoit, High Temperature Mechanical Behaviour

of Ti(C,N)-Mo-Co Cermets,

Int.

Re$-.

Met&Hard Mat.

16 (1 998) 257-68.

(13)

Z. Zackrisson,

Rolander, G. Weine,

Andren, Microstructure of the Surface Zone in a

Heat-Treated Cermet Material,

Int.

Refi.

Met&Hard Mat.

16 (1 998)

15-22.

(14)

Liuying, L. Huayi, B. Hengzhen, L. Gouchun,

Influence

CH4/N2 ratio on microstructure and

mechanical properties

PCVD-Ti(C,N,-,),

Znt.

Refi. Met&Hard

Mat.

995) 369.

H. Pastor, Titanium Carbonitride-Based Hard

Alloy for Cutting Tools,

Materials Science and

Engineering,

A105/106 (1988) 401-9.

(16)

Zhang, C. D. Qin,

C. Limy Solid Solution of

WC and TaC in Ti(C,N) as revealed by Lattice

Parameter Increase,

Int.

Refi.

Met&Hard

Mat.

(1993-94) 329-33.

Bellosi,

Medri, F. Monteverde, Development

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submitted to the

Am. Cer. Society.

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Lawn,

D. B.

Marshall,

Critical Evaluation of Indentation

Techniques for Measuring Fracture Toughness, 11,

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64 (1992)

539-43.

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SENSITIVITY CHARACTERIZATION TO FLAMMABLE

GAS

Precursor

Deposition

Seong -Eun Sim, Sung-Churl Choi

a-Fe203 Sn02

Fe(C0)s SnCL

175

C 350 "C

Department

Ceramic Engineering Hanyang University

Seoul 133-791, South Korea

Temperature

Deposition

ABSTRACT

3,s minute l,2,5,8,10 minute

There has been considerable interest in recent

years in thin film

gas

sensing materials. In comparison

with conventional sintered bulk gas sensor, thin film

gas

sensor materials have

good

sensitivity, optimum

temperature and selectivity. The use of tin oxide based

materials

gas sensing elements for a wide range of

reducing gases has been extensively studied. Since the

electrical conductivity of tin oxide (Sn02) thin film

changed by adsorbing gases, such as

H:,

C&,

LPG,

has been applied for

gas

sensors. The SnOz is a n-hpe

semiconductor in which excess electrons produced by

o.xygen deficiency act

donors and therefore

electrical conductivity depends on the changes of its

lattice defects. The femc oxide (a-Fe203) has

attracted interest of investigators

a material for

semiconductor

gas

sensors.

This

interest is connected

with the properties of a-Fe203 which

has

a good gas

sensitivity, a good long term stability and a lorn

humid-effect without the application of noble metal

doping.

EXPERIMENTAL

this

study, the gas sensing device was fabricated

by CVD. The fabrication process

was

follows: first,

washing the polished alumina substrate for the

improved bonding effect. Second, sputtering the

electrode

0,300

the front. Third, coating

Fe203 at 175 "C and

Sn02

at 350 "C.

Fourth,

heat

treatment at various conditions.

Fifth,

bonding

the

Ni-

Cr wire on the back. Si'uth, sensitivity measurement

and analysis.

Fifth,

bonding the Ni-Cr vire on the

back. Sixth, sensitibity measurement and analysis.

Following the reaction to a-Fe2031Sn02 of

deposing device.

4Fe(CO)s+1302

2Fe203

20C02

SnC14

SnO-,

2 Ci

reaction ratio of the Ar and

was

controlled by

MFC

(Mass

Flow

Controller, MKS.Co.,)

Flon7 of Reactant

Flow of Carrier

Output Pressure

Vapor Pressure of Reactant

Pressure

ton

Flow Rate

106:

26sccm

197

17 sccm

Table 1: Deposition conditions of variable factors

Table 1 is shoning deposition conditions. The

gas

sensikity to flammable gases (C&,

H2,

LPG)

was

measured. The sensitivity

"S"

gases

is defined here

k,,

where

and

RgaJ

are the

sample resistance in clear air and in air containing

testing

gases

respectively.

This

device was heat

treated at

400

"C,

450

"C,

500

"C,

550

"C,

600 "C for

2hr

enhance the gas sensitivity. The heat treated

deh-ice at

500

for

2hr

had the best properties and

especially shows high sensitivity to

gas.

The

figures 1 and 2 are showing the

SEM

morphology.

The sensitivity to gases

was

studied in the temperature

range from

100

300

"C in order to find the

optimum detection temperature. The optimum

temperature was 175

"C.

Fig

heat treatment

Fig.

Heat treatment at

500