Removal of low molecular weight constituents during thermal debinding of MIM compacts

Hard materials and tool steels SINTERING CHARACTERISTICS OF TUNGSTEN CARBIDE-SILICON CARBIDE-NICKEL HARD MATERIALS S.H. Cho et al (Inha University, Inchon, Korea), J. Korean Inst. of Metals, Vol 32, No 7, 1994, 786791. (In Korean). The development of a WC alloy with a Ni matrix and aditions of Tic and Sic was reported. The processing included coating of the WC particles with Sic before sintering. Grain size was 1-2 urn and Vicker’s hardness was 1600. Sic was reported to inhibit mobility and TiC to inhibit grain growth by restricting solution/precipitation of WC in the Ni. The high hardness is attributed to solid solution hardening. CEMENTED CARBIDES WITH RARE EARTH ADDITIONS L. Guihua et al (North Eastern University, Shenyang, China), PM Technology, Vol 12, No 3, 1994, 206-209. (In Chinese). Production, structure, physical and mechanical properties and cutting performance of a cemented carbide with rare earth addition were investigated and compared with a similar material without the addition. It is reported that the bend strength and durability is increased by the addition of rare earths. In termetallic compounds and materials MECHANICAL AND OXIDATION PROPERTIES OF TITANIUM ALUMINIDE WITH TITANIUM CARBIDE S. Ochiai et al (Nishi Tokyo University, Yamanashi, Japan), J. Japan Sot. Powder and Powder Metallurgy, Vol 41, No 2, 1994, 170-175. (In Japanese). An investigation of the incorporation of 5~01%Tic in Ti Al, 42at%Al, is described. Elemental Ti, prealloyed TiAl and graphite were mechanically alloyed and hot pressed. TiC formed during MA and was dispersed in 5 to 10 urn particles in the TiAl matrix of the sintered alloy with some AlaOs. The alloy was reported to have good ductility up to 900°C and good oxidation resistance.

Mechanical alloying STRUCTURAL BEHAVIOUR AND PROPERTIES OF MECHANICALLY ALLOYED ALUMINIUM ALLOY POWDER X.X. Yan et al (University of Paris Sud, Orsay, France), Rev. de Metall., Vol 91, No 5, 1994, 733-744. (In French). The use of MA in PM is discussed with reference to amorphous and oxide 40

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dispersion strengthened materials. An investigation of processing A1-4.4wt%Cu0.5%Mg-0.4%Si powders by MA is the intention being to described, determine the characteristics of the milled powder. Processed particles, with a line grain size, are shown to consist of fragments welded together. It is deduced that the incorporation of Cu in the Al matrix is complete. Shrinkage of specimens pressed at 400 MPa is noticeable at 620°C. The properties are reported to be superior to those of conventional PM materials. MATHEMATICAL TREATMENT OF PHYSICS OF MECHANICAL ALLOYING IN PLANETARY BALL MILL M. Abdellaoui, E. Gaffet (Inst. Polytechnique de Sevenans, Belfort, France), Acta Metal. Mater., Vol 43, No 3, 1995, 1087. 1098. Kinematic modelling of mechanical alloying in a planetary ball mill is described and equations giving ball acceleration and velocity are given and discussed. Energy transfer in collisions, shock frequency and injected shock power are calculated. Comparison with published data shows that neither shock energy nor frequency were taken into account. MOSSBAUER STUDY OF BALL MILLED COBALT-IRON-SILICON-BORON POWDER A. Calka et al (Australian National University, Canberra, Australia), Nuct. fnstr. Methods Physics Research B, Vol 76, No l/ 4, 1993, 81-84. A study of ball miiled amorphous Co-FeSi-B powder, using Mossbauer effects and X-ray diffraction, is described. Powders are shown to be amorphous after 50 hours milling with a ball-to-powder ration of 84. The powders are shown to contain structural and chemical imhomogeneities when compared with the melt spun ribbons from which they were ‘made. SYNTHESIS OF AMORPHOUS AND METASTABLE TITANIUM-ALUMINIUM ALLOYS BY MECHANICAL ALLOYING W. Guo et al J. Mater. Science, Vol 29, No 9, 1994, 2436-2444. It is reported that amorphous and metastable products have been made by planetary ball milling of elemental TiGOat%Al powders. The structure of the product depended on ball size and varied between amorpous solid solution of Al in ETi and disordered TiAl compound.

Metal injection moulding SQUARE ROOT WICK DEBINDING MODEL FOR POWDER INJECTION MOULDING R. Vetter et al (Delft University of Technol-

ogy, Delft, The Netherlands), Powder Metallurgy, Vol 37, No 4, 1994, 265-271. A model of wick debinding is reported to show a square root relationship between degree of debinding and time, agreeing with experiments. The model basis is inverse flow of phase separation at the binder-air interface. Two sided debinding is shown to be twice as fast as single. Effect of variation of binder viscosity is considered. A discrepancy was noted in previous predictions and experiment. This is attributed to capillary pressure difference and permeability drop due to ‘artery’ formation in the draining compact. EFFECT OF BINDER COMPOSITION ON INJECTION MOULDING OF STAINLESS STEEL POWDER KC. Hsu et al (National Taiwan University, Taipei, Taiwan), Powder Metallurgy, Vol 37, No 4, 1994, 272-276. The effects of a range of waxes on MIM of 304L stainless steel with a low density polyethylene based binder was investigated. Binder phase separation with some waxes was reported. Binders with carnuba wax or acrawax appeared to be more satisfactory than those with paraffin or polyethylene waxes due to higher viscosity and better pseudoplasticity. All the waxes gave specimens with a good surface finish. Highest tensile strength was found in the mixture with paraffin wax. REMOVAL OF LOW MOLECULAR WEIGHT CONSTITUENTS DURING THERMAL DEBINDING OF MIM COMPACTS H.H. Angermann, 0. van der Biest (Katholik University of Leuven, Heverlee, Belgium), Int. J. Powder Metallurgy, Vol 30, No 4, 1994, 445-452. Two-component binders based on polpropylene with either non-polar paraflin wax or polar stearic acid, both with low molecular weight, were investigated with reference to removal of the low MW component during lower temperature thermal debinding of 316 L stainless steel. Less removal of the paraffin wax, due to interaction with polypropylene, was reported. Effects of debinding conditions were described. It is shown that the removable weight influences total debinding time and must be taken into account in fixing the time.

Metal matrix composites MACRO-SEGREGATION DIAGRAM FOR DRY BLENDING PARTICULATE METAL MATRIX COMPOSITES J. Ivengar et al (Carnegie Mellon University, Pittsburg, Pennsylvania, USA), ht. J. Poude-r Metallurgy, Vol 31, No 1, 1995, 37-49. Blending of metal and particle reinforcement powders for composites is