Mechanisms of hydrogen reduction of molybdenum oxides

Hardmetals - microstructural testing and property maps B.Roebuck

et

(National

al.

design

Physical

Laboratory,

Teddington, UK.)

It was noted that the technology WC-Co

presented. It was noted that pore shape change

ofTiCofTi(C,N),

affects densification

0.2 to0.7wt%.Alloyscon-

conventional

have led away from the

two-phase structure. The poten-

of microstructural

improvements changes

in particle

distribution. and the

design

and property

were discussed with reference to size and shape and phase

Testing procedures were reviewed

move

towards

performance-related

tests, such as wear, and their ability to discriminate the effects of structural variations was outlined. The

concept

of property mapping was

introduced as a means of optimising properties.

Transition for high-speed to solid carbide tools K.Friedrichs.

(Konrad

Friedrichs

steel tools

ed in the continuum

materials had promising combinations

The models are based on those of Gurson and

of hard-

used. Predicted

Factory,

Kuhnbach, Gemwny.)

Developments presented

in solid carbide

with reference

Effect of binder volume fraction gradient sintering of cemented carbides R.Frykholm

et al. (Chalmers

tools were

to these as replace-

ments for high-speed steel tools, tougher types

University

tribution

on

of Technology,

It was noted that cemented carbide tools may be coated to increase cutting performance

and

that cracks may be introduced during coating. cracks propagating

into the sub-

machines.

12)%Co

Toughness

and higher

of WC-

toughnesses

(10 or

were dis-

cussed. Use of screw extrusion was reviewed.

L.A.Cornish

et

al.

(University

Johannesburg,

South Africa.)

of Witwatersrand,

Fifteen different V-W-Co-C tered at 1450°C

alloys were sin-

for five hours and quenched.

Structures contained (V,W)Cx

particles in a Co

matrix with a carbide eutectic phase. The composition of the (V,W)Cx

phase was determined

University

of Technology,

It was reported

that very large, plate-like,

WC grains, above 20mm, formed during sintering of WC-Co

from 100 to 200nm powders.

The growth of these crystals was investigated with respect mechanism

to temperature. involved

The

intermediate

proposed formation

of h carbides, M 12C and M6C.

B.Lux

et al. (Vienna

University

of Technology, Vienna,

AUXli4l.)

Literature concerning

formation and growth

of trigonal shaped WC platelets was critically reviewed and mechanisms tion were identified.

for platelet

Based on this

www.metal-powder.net

forma-

a process

Ilmenau,

Use

of inductively

coupled

plasma

tech-

niques was discussed and it was shown that this

made by impinging the powder on to a suitable

of sintering

of WC-

for 5.0, 6.7, 10 and 2Ovol%Co.

It

was shown that formation of gradient structures is controlled

substrate,

a labyrinth factor, 1, is introduced

to improve

agreement between experiment and simulation.

changing

the composition

can be as the

coating is built up.

Mechanisms of hydrogen reduction of molybdenum oxides W.G.Schuhneyer,

Low-pressure boron nitride R.Haubner,

Layered structures

by diffusion in the binder phase

but limited by dispersed particles. In the model

deposition

H.M.Ommer.

Technology, Darmstadt,

of cubic

(Darmstadt

‘Z.Tang. (Technical

University

An investigation

of Vienna,

niques,

University of

Germany.)

of reduction

H, using thermogravimetry as functions

of MOO, by

and other

tech-

of process and material

parameters, was described. Depending on con-

The paper asked the question:

’ Is chemical

ditions various mechanisms

and intermediate

vapour deposition of cubic BN possible?’ It was

products were identified. Under all conditions

noted that low-pressure deposition of diamond

the first stage is Moo3

had been possible and the possibility of a simi-

Shape and size of MoOz particles depends on

lar process for cBN was considered. Some early

H,O

attempts failed due to problems in characteris-

stage depends on dew point and two reaction

ing the deposits. A chemical vapour deposition

paths were found, pseudomorphic

reactor

tion or chemical

was used and deposits

terised by a range of techniques. that the existence

were charac-

I? Wilhartitr.

of the atmosphere.

et al.

(Plansee

AG,

Reutte,

of Mo in electronics were noted.

Use of pure MO is limited because of low resis-

(University

grains,

pores,

Warsaw,

of these may vary according to process route. It by image

analysis

which provide data concerning microstructural

elements

0.5mm, can be protected against low tempera-

sintered samples was presented.

the number of

was described

and a

of microstructure

of

at least

Simulation of hot forming of refractory metals using porous metal plasticity models of sintered forming,

Oxygen concentration and defect structure in molybdenum and tungsten B.A.Gnesin

et al. (Inst.

Chemogokwka,

Solid State Physics of RAS,

Russia.)

It was reported that neutron activation analy-

E.Parteder et al. (Plansee AG, Reutte, Austria.)

during hot

methodology

and stereology

and spatial distribu-

tion. The

for densification

and

was shown that these can be quantitatively

method for optimisation

by alloying with Re,

of sintered metinterphases

grain boundaries, were identified. The amounts

tance to corrosion in moist air even at ambient

metals,

transforma-

of Technology,

temperatures. It was shown that thin films, up to

refractory

The second

vapour transport.

Features in microstructures als, particles,

analysed

Two models

MoOz.

Poland.)

Austria.)

Applications

Mo40,,+

Quantitative description of microstructure of sintered metals J.J.Bucki

Protection of thin film molybdenum and alloys against low-temperature oxidation A.Schintlmeister,

content

+

It was reported

of cBN crystallites had been

lOwt%, or by coating with a thin layer of MoOz.

tungsten

University,

and nano-powders.

ture corrosion

Hardmetals containing carbide platelets

(Technological

tally and by simulation

General topics

(Vienna

et al.

carrier gas to make a range of oxide ceramic

Growth of large crystals of tungsten carbide during sintering ultrafine tungsten carbide et al.

G.Nutsch Germany.)

dient surface layers was investigated experimen-

verified by transmission electron microscopy.

MSommer

Production of ultrafine powders and layered nano-structures

can be used with various additives to the Ar-0

surface layer. Formation of gra-

and related to microhardness and structure.

Vienna, Au&a.)

density dis-

gen-containing

Vienna, Austria.)

Effects of composition of (vanadium tungsten) carbide in vanadiumtungsten-cobalt-carbon

and experimental

data are compared for a hot-formed

strate a tough surface can be created by a nitro-

of carbide, coating procedures and high-speed cutting

description.

MO disc.

Gliteborg, Sweden.)

To prevent

constitutive

Golaganu et al. Finite element procedures were

ness and toughness.

Ti(C,N)-Co Carbide

and this should be includ-

tained platelets with aspect ratios of 1:lO. The

hardmetals is well established and that

recent developments tial

of making

route was evaluated. This involves the addition

were

sis had been used to determine 0 in commercial and high purity MO and W. The 0 content was

MPR

September

2002

39