Structure and properties of mechanically alloyed copper-chromium alloys

Powder production PRODUCTION OF FINE METAL POWDER BY GAS ATOMIZATION L. Gang et al. (Chinese Academy of Sciences, Beijing, China.) PM Technology, Vol 14, No 3, 1996, 181-186. (In Chinese.) Gas atomization of fine metal powders is discussed with reference to the results of a study. Powder from a close coupled high pressure atomizer is reported to be spherical, to have a low 0 content and to flow easily. High atomization efficiency is reported.

Pressing PARTICLE DYNAMICS SIMULATIONS OF STRUCTURES IN NANO-POWDERS A. Misra. (University of Missouri, Kansas City, USA) Mater. and Manuj Processes, Vol 11, No 6, 1996, 925-934. A study of behaviour of powder particles, less than 50 urn in size, characterized by low relative density, high dispersivity and exhibiting particle clustering, is described. Morphology is influenced by interparticle interactions arising from van der Waals forces. A potential function, which describes interactions between spherical nano-particles, is deduced. A computer simulation of equilibrium structures at various densities was developed and used to study powder compaction. HIGH PRESSURE COMPACTION AND SINTERING OF NANO-SIZED ALUMINA POWDER B. Hockey et al. (National Inst. of Standards and Technology, Gaithersburg, USA.) Mater. and Mar@ ProcesSes, Vol 11, No 6, 1996, 951-967. Effects of pressure, up to 5 GPa, on compaction and sintering, in the range 1900 to 16OO”C, of nano-sized AlaOs were investigated. Green density was increased by increased pressure. Below 3 GPa there was significant porosity in all sintered specimens which was related to the a/? transition. Above 3 GPa this did not occur and near full density, with a grain size of 150 nm, was attained. CONSOLIDATION OF NANOCRYSTALLINE ALUMINA S. Kwon et al. (Pennsylvania State University, Pennsylvania, USA) Mater. and Manu$ Processes, Vol 11, No 6, 1996, 969-985. It is reported that dense aAlaOy had 42

MPR April 1997

been fabricated from seeded nanocrystalline boehmite powder. To avoid problems gel agglomeration powders were dispersed in ethanol. Homogeneous green structures and high sintered density were

attained by dry pressing. A superplastic phenomenon was used to produce fully dense transparent AlzOa by sinter forging. Microstructural evolution and densification were correlated with the effects of seeding and compaction pressure.

Sintering SIMULATION AND.EXPER1MENT.S ON SINTERING OF NANO-PARTICLE POWDERS H. Zhu, R.S. Averbach. (University of Illinois, Urbana, USA) Ma&r. and Man& Processes, Vol 11, No 6, 1996, 905-923. Simulation and experiments on sintering of nano-sized Cu powders are described. Molecular dynamics and differing shapes were studied. It is shown that sintering can be rapid due to high shear stresses at interparticle contacts. Particle rotation is demonstrated, forming low angle boundaries. Full densiflcation only occured when the particle assembly was close packed. Experiments on TiOz are described and a densification law presented. LATTICE DIFFUSION FROM GRAIN BOUNDARY IN SINTERING OF METAL POWDERS R.L. Eadie, X. Chen. (University of Alberta, Edmonton, Canada.) Int. J. Powder Metallurgy, Vol 32, No 3, 1996, 265-275. Sintering maps and lattice diffusion to sintering necks are discussed. Published solutions for diffusion are reviewed with respect to weaknesses. Two new solutions are proposed. One with maximum curvature at the sintering neck and the other with variable curvature. Applicability is considered with reference to lattice and boundary solutions. The effcts on sintering maps is discussed.

Fundamentals

reference to densification maps, plastic yield, creep and diffusion. The need to extend densification maps to nano-sized powders is noted. Existing maps predict that nm powder dens@ more easily than pm powders but this is not observed in practice. This is attributed to failure to consider powder agglomeration and surface diffusion. STUDY OF COEFFICIENTS IN YIELD FUNCTIONS MODELLING METAL POWDER DEFORMATION T.C. Tszeng, W.T. Hu. (Scientific Forming Technologies Carp, Columbus, USA) Acta Materiallia, Vol 44, No 9, 1996, 3543-3552. Phenomenological constitutive models of compaction, on the basis of continuum mechanics are discussed. Behaviour of loose and sintered powders are compared. One model is examined with regard to coefficients required to describe powder behaviour during pressing and applied to standard and proportional triaxial compaction of two powders, widely differing in morphology. A new model is proposed to take particle shape and stress state into account.

Aluminium PHASE TRANSFORMATION OF MECHANICALLY ALLOYED ALUMINIUM-CHROMIUM POWDERS J.S. Lee, S.I. Kwun. (Korea University, Seoul, Korea.) J. Korean Inst. of Metals, Vol 34, No 4, 1996, 433-439. (In Korean.) Phase stability of Al- (lo,15 or 48) at%Cr, after mechanical alloying for 2000hours and heat treatment, was investigated. AllO%Cr contained an Al solid solution and a Cr phase after MA and transformed to AlAll&r2 after heating at 460°C. In Al-15%Cr after heating at 460°C All&r2 and an amorphous phase were present. A&r2 and AlsCra were found in AICrz after heating. Vacuum hot pressing at 460°C gave amorphous compacts.

Copper

DENSIFICATION MAPS FOR NANOSIZED POWDERS

STRUCTURE AND PROPERTIES OF MECHANICALLY ALLOYED COPPERCHROMIUM ALLOYS

M.G. McKimpson. (Michigan Technological University, Houghton, USA) Mater. and Manu$ Processes, Vol 11, No 6, 1996, 935949. Densification mechanisms in particle 1 urn or larger in size were discussed with

W. Erde et al. (Harbin Inst. of Technology, Harbin, China.) PM Technology, Vol 14, No 3, 1996, 175-180. (In Chinese.) It is reported that Cu-5%Cr powders had been prepared by MA of elemental powders and consolidated by hot hydrostatic

extrusion. Microstructure and properties are described and discussed. Strength of 750 MPa is attributed to fine grain structure and dispersion strengthening. Ductility of 8%) and conductivity of 60% were found after heat treatment.

CHARACTERIZATION BORON O.A.

AN:D

OF PM ULTRAHIGH

et

al.

(National

Metallurgical

Investigations,

Spain.)

and

Metall.

Centre

for

Madrid,

‘I’rans A, Vol

Ma&r.

Investigations alloys

of

and

and

fine

use

H tool

made

of

prepare

properties

were

powders

the

PM to

ultrahigh

good mechanical Compacts

steels

rapid Fe-B

gas atomized

by HIP at 700 to I lOO>C to yield a temparatures

Lower

gave optimum mechanical which are described.

EFFECTS OF TIN ON PROPERTIES OF IRON BASE ANTIFRICTION ALLOYS WITH MOLYBDENUM

DISULPHIDE

M. Chandrasekaran, I’. Singh. (Indian Inst. of Technology, Madras, India.) Int. J. Vol 32, Ntr 3, 1996,

Pwwde-r Metallurgy. 323-330.

that

had been fabricated

Fe CuPb-MoSz-Sn

by PM methods.

The

addition of Sn is shown to enhance mechanical and antifriction properties up to

1.75wtXSn

and

deteriorate.

above

1.75%&i

dimensional

this

gave

the

properties smallest

DYNAMIC

T. Jun et al. (Chinese Academy of Sciences, Shanghai, China.) PM Technology, Vol 14,

Japanese.)

formation

of finely

increases

properties.

Crack

tests

In Chinese.

behaviour

to thermal

PROPERTIES

OF

HEAVY ALLOYS

.J. Korean

Inst.

No 4, 1996, 447-456. Adiabatic

shear

testing.

stress increased are reported

in W-4.9%Ni-

by dynamic torsion

were

treated,

and

oj‘Metals, Vol 34,

banding

Tests

heat

specimens

Carp, Kyungju,

(III Korean.)

2.1%Fe was investigated

performed

swaged

maximum

and

dynamic

on

toughness

are

is discussed

with

regard

expansion.

Composite

F. Ajersch

OF

et al. J. of‘Metads, Vol 48, No 6,

1996, 56-59. A vacuum described and the

plasma is shown

production

of

matrix

composites

ceramic

particles

technique to be suited

near

is to

net

shape

Al-

reinforced

with

fine

which

are reported

to

be uniformly dispersed. Bulk porosity was less than 1.5%. Mechanical properties of the

materials

Investigations

were

increased

by plastic

deformation.

of Tokyo,

and Powder

of fracture

materials

Fragmentation was studied

of

described.

of samples

geometries.

(In

toughness

are

for different

of WC-lOwt%Co

specimen

Results

are

with

particular

and test

expressed reference

to a shape factor, &,.

CARBIDES

FORMING

(University

Vol 42, No 4, 1995, 417-421.

Metallurgy,

hard

FOR HARD

Sot. Powder

SINTERABILITY

materials

NEAR NET SHAPE

J.Japan

mathematically

described.

OF CEMENTED

WITH ALUMINIUM

ADDED

TO BINDER

PHASE

M. Fukunaga

et al. (Kobe Steei Ltd, Akashi,

Japan.)

J.Japan

Sot. Powder

and Powder

Vol 42, No 4, 1995. 422-426.

Metallurgy,

(In


or

Fe)

investigated. poor

and oxidation

with

WC-Co-Al

sinterability.

densified strength

well

of WC-(Co,

additions

of

Al

is reported

WC 11.2wt%Ni-0.7%Al

to

a transverse

rupture

of 2.1 GPa and Rockwell

hardness

of 9OA Higher values were attained 8.6%Fe-1.4%Al. oxidized

were

to have

The

Fe

and

for WC-

Ni

alloys

less than the Co alloy.

EFFECT

OF TUNGSTEN

BORIDE

ADDITION ON SINTERING OF CHROMIUM CARBIDE-NICKEL

Electrical and magnetic materials

CERMETS

in this tuder. Observations of

NON-TRADITIONAL ELECTROCHEMISTRY

AND

Lavrenko. Pomshkovaya Electrochemical

theory

is reviewed

in sulphuric

oxidation acid

Metallurgiya,

(In Russian.) of

(In Russian.)

reviewed, work which is reported

1250 to

improved

materials.

liquids,

spherical

abrasive

powders

Magnetic

magnets

pseudo-

and

magnetic

are discussed.

SINTERING

COMPACTED

as

formation bonding

a

the

high to allow

a

sinter

It is shown that

sintering

sintering of

enhancer

and

temperature

liquid

phase.

by

Sinter

is possible.

STRUCTURE

AND PROPERTIES

OF

MOLYBDENUM-NICRELBORON-

OF SHOCK

VANADIUM

TITANIUM-CARBON

HARD ALLOYS

Y. Yamasaki HA Grebe et al. (TEX-TUBE Co., Houston, Texas, USA) Metall. and Mater. ‘Frans A,

Kudamatsu,

Vol 27A, No 7, 1996, 1749.1759.

438-442.

that

shock

pressed

contained

to promote

sintering controlled compacts Knoop

shock and by

reactive

sintering.

compaction

that

the

diffusion.

synthesis The

was

1360

is

sintered

were of near net shape hardness

It is

enhanced

and the to

1935.

Kohan

J.Japan

Co. Lyd.,

Sot.

Powder

(In Japanese.)

Microstructures

compression

properties

that

et al. (Toyo Japan.)

and Powder Metallurg?/. Vol 42, No 4, 1995,

had been used to prepare dense compacts from ‘T-C powders. The compacts were hot

of W and corrosion Limiting

acts

and

MIXTURES

and a study of high

is, described.

WB

Co., KudaPowder

that Cr.&, sintered well at

13OO”C, too

bonding to steel substrates. reduces

Hard materials and tool steels REACTION

It is reported

Sot.

Vo142, No 4, 1995,432.

Powder Metallurgy,

to lead to

Kohan

J.Japan

437. (In Japanese.)

shown heat

et al. (Toyo

matsu, Japan.)

Studies of fabrication, structure and properties of hard magnetic materials are

It is reported

OF MATERIALS

No 7/8, 1995, 107-120.

temperature

K. Nakano

Metallur-

shear bands is greatest in

swaged and aged bar.

CORROSION

MATERL4LS

Poroshkovaya

aged shear

to show that the possibility

forming adiabatic

resistance

TiBs which

Fracture

giya, No 7/8, 1995, 68-83.

KJ. Park et al. (Poongsan

VA

between B& results in

dispersed

results

L.N. Tulchninsky.

TORSIONAL

TUNGSTEN

sintered,

Y. Yanaba, KHayashi. Japan.)

It is reported that reaction and TIC during processing

EQUATIONS

change on sintering.

Tungsten

bar

BORON

CARBIDE

bend

IN FRACTURE

TOUGHNESS MATERIALS’

PM HARD MAGNETIC

Korea.)

of the TiC are described

COEFFICIENTS

ALUMINIUM MATRIX COMPOSITES BY THERMAL PLASMA SPRAY FORMING

properties

Characteristics and discussed.

is outlined.

with

are described.

from

microstructure.

It is reported

are discussed for a Effect of polymer

Ceramics

and

27A, No 7, 1996. 1861~1867. solidification

coatings

No 3, 1996, 168-174.

STEELS

Kuano

in H evolution of materials.

TOUGHENING OF TITANIUM DIBORIDE BY IN SITU FORMED

Iron and steel PROPERTIES

factors range

12.5) “# particle

of alloys

and

mechanical

Ni-6wt%B-58.6%Mo-(0 were

MoaNiBa size with

investigated. which

increase

to Alloys

decreased

in

in “%V. This

is

in crystal structure from orthorhombic to tetragonal. Highest transverse rupture strength. 2.5 GPa. was attained at 12.FjW. attributed

to a change

MPR April 1997

43