Oxidation, under isothermal and cyclic conditions, of Fe-(0 to 30)wt%Cr and Fe-(0 to 30)%Cr,(O to S)%Si coatings, laser deposited on Fe substrates, was investigated by thermogravimetric analysis at 800 to 1000 “C and structure determination of the oxide deposit. Si is reported to increase oxidation resistance. Binary Fe-25%Cr and ternary Fe- 12%Cr-2.5%Si coatings had similar oxidation resistance.

green strength and flexibility to allow han- dling. Mechanisms and analysis of organic

binders, added to the powders, were investi-

gated. Physical characteristics of the green

tapes were described, with regard to

process and material parameters. The object

of the study was to make a thermo-electric generator from multiple layers of different

material.

Current state of diamond coated cutting tools

K.Kn&. J. Surface Finish. Sot. of Japan, Vol51, No 3,

2000, 238-242. (In Japanese.)

Composite materials Hard materials and tool steels

The current state of the art of diamond

coated cutting tools is reviewed with respect to performance for various cutting

geometries. Increased demand for coated

tools for cutting a wide range of metallic, non-metallic and composite materials is

discussed.

Types, properties and applications of metal matrix composites

J.M.T.Castello et al. (University of C&OS III, M&id,

Spain.) Revista Metall. Madrid, Vol 36, No 3, 2000,

179.192. (In Spanish.)

Effect of pre-alloyed materials on microstructure of titanium-tungsten carbonitridecobalt

Microstructure and properties of tungsten carbide-cobalt with triangular prismatic grains

The current state-of-the-art of metal matrix composites, used in automotive and aerospace applications, is reviewed. The materials con- sidered are based on Al, Ti and Mg alloys with particulate or fibre reinforcements. Types of composite are identified and properties and applications are discussed.

H.O.AndrCn et al. (Chalmers University of Technology,

GBteborg, Sweden.) Int. J. Refractory Metals/Hard

Mater., Vu1 18, No 6, 2000, 273-279.

K.Hayashi et al. (Uniuersiry of Tokyo, Tokyo, Japan.) J.

Jpn Sot. Powder/Powder Metall., Vol47, No 5, 2000,

526-533. (In English.)

Synthesis of nano-composite tungsten carbide-magnesia

Materials were prepared from Tic-XN-

WC, Ti(C,N),WC, (Ti,W)-TiN and

(Ti,W)(C,N) mixtures and characterized for

structure. Alloys made from binary mixtures had finer grain sizes and less homogeneity. Alloys with WC showed core-rim structures.

Thermodynamics was used to show com-

pounds formed during solid state sintering at 900 “C in low N activities.

MS. el Eskandarany et al. (Al Ahmr University, Cairo,

Egypt.) M&l/Mater Trans A, Vol 32A, No 1, 2001,

157-164. Dispersion of tungsten carbide-cobalt powders in aqueous media with polyethylenimine

It is reported that methods for production

of WC-Co, with WC grains in a triangular

prism morphology, had been developed. W

and C powders are used instead of WC.

Processing is conventional. It was found

that the (0001) planes of the WC are oriented

parallel to the direction of compaction.

The new alloy is reported to have higher

fracture toughness and transverse rupture

strength than conventional WC-Co at the

same %Co.

It is reported that a nano-composite WC- MgO powder had been prepared by high energy ball milling of Mg-C-WO, powders in Ar at ambient temperature. Initially C and WO, particle become embedded in Mg parti- cles followed by reduction to W and oxida- tion to MgO. Finally W combined with C. This powder was consolidated by vacuum pressing and plasma activated sintering to a density of 99.5%. It was nano-crystalline with a grain size below 50 nm. Vickers hard- ness was 15 GPa and fracture toughness 14 MPa.m112. Applications for rock drilling were noted.

E.LMrz, L.Bergstriim. (Inst. for Surface Chemistry,

Stockholm, Sweden.) Int. 1. Refractory Metals/Hard

Mater., Vol 18, No 6, 2000, 281-286.

Corrosion of tungsten carbide-chromium carbide-nickel by potentiostatic polarization

Y.Hay& et al. (Kyushu University, Fukuoka, Japan.) J.

Jpn Sot. Powder/Powder Metall., Vol47, No 5, 2000,

541-546. (In Japanese.)

Application of molybdenumcopper composites

Use of suspensions of WC-Co powders in

fluid media in PM processing of hardmetals is

discussed and problems, in use of water, are noted. Use of polyethylenimine, PEI, as a dis-

persant was investigated. Powders were wet

milled, dewatered and mixed with PEI and

water. Rheological properties of the suspen-

sion were measured and decomposition of PEI

was investigated. It is considered that PEI is a

suitable dispersant for WC-Co in aqueous

media.

Corrosion of WC-Cr,C,-Ni materials

was investigated by potentiostatic polariza-

tion techniques in acid and neutral solutions.

Unusual peaks in the polarization curves

were found. Corrosion resistance was found

to be highest at low %C and high %Cr,C,.

This is attributed to passivation due to increased W and Cr dissolved in the Ni

binder.

D.M.Lu. (Central Iron/Steel Research Inst., Beijing,

China.) Powder Metall. Industry, Vol IO, No 6, 2000,

30-33. (In Chinese.)

Wear mechanisms for cubic boron nitride in cutting iron-graphite compacts and grey cast iron

Mechanical alloying

Production, properties and applications of MO-Cu composites are described.

H.M.Ortner et al. (University ofTechn&g?, Darmstadt,

Gemurny.) Int. J. Refractory. Metals/Hard Mater., Vol

18, No 6, 2000, 287-296.

Reactions and amorphization in mechanically alloyed zirconium-aluminiumcopper-nickel

Electrical and magnetic materials Characteristics of green thermo-electric tapes

H.Robertson et al. Materials Chemistry/Physics, Vol62,

No 2, 2000, 263-272.

It is reported that tapes had been prepared from thermo-electric powder alloys.

Process variables were optimized for enough

Wear mechanisms of cubic BN, used

in cutting Fe-graphite compacts and grey

cast iron were investigated. Mechanisms

identified were oxidation of the tools

and interdiffusion of constituents between

tool and workpiece, and were similar for

both Fe alloys. Tool life was greater for cast

iron due to MnS, which acted as a lubricant

and a diffusion barrier giving reduced tool

wear.

J.Eckert et al. (Fraunhofer Inst., Dresden, Gemuny.)

Acta Mater., Vol48, No 14, 2000, 3657-3670.

Amorphization in elemental Zr-

7.5at%Al-17.5%Cu-lO%Ni powders was

investigated and was shown to take place

by solid state reactions. A layered structure

of pure elements was observed initially.

Alloying between layers was, to some

extent, by anomalous fast diffusion of small

atoms. It is suggested that dislocation pipe

diffusion is an important mechanism.

40 MPR November 2001 www.metal-powder.net