composites are described. Characteristics of the materials, depending on composition, process and service conditions are discussed. SYNTHESIS OF NANOAMORPHOUS ALLOYS BY PARTICLE CONDENSATION AND COMPACTION R. Wiirschum et al. (University of Stuttgart, Stuttgart, Germany). Nanostructured Materials, Vol 6, No l/4, 1995, 377-380. It is reported that the technique of sputtering and particle condensation has been applied to the preparation of amorphous Ni-Zr and Ni-Ti alloys.
Titanium STRUCTURES AND MECHANICAL PROPERTIES OF SINTERED TITANIUM-CHROMIUM ALLOY K. Suguya et al. (Kyushi University, Fukuoka, Japan). J. Japan Sot. Powder Powder Metall., Vol 41, No 8, 1994, 964-969. (In Japanese.) It is reported that a Ti-13wt%Cr alloy was made from mixed elemental powders by pressing and sintering just above the eutectoid temperature. Structures and properties were determined and related to the phases precipitated during cooling. Three phases were detected, c(, w and residual 8. Slow cooled specimens showed embrittlement which could be reduced by oil quenching at SOdegC.min-‘.
Coatings on hardmetal
TECHNOLOGY PERSPECTIVE ON CHEMICAL AND PHYSICAL VAPOUR DEPOSITS ON METAL-CUTTING TOOLS D.T. Quint0 (Kennametal Inc, Latrobe, Pennsylvania, USA). ht. J. Refractory Metals Hard Mater., Vol 14, No l/3, 1996, 7-20. Developments in chemically and physically vapour deposited coatings on tools for metal-cutting are reviewed. Comparison is made between multi-layer CVD and single layer PVD coatings and a combined process. Failure mode diagrams are considered as a framework for tool design, operating environment and the synergy between coating and substrate. COMPARATIVE EVALUATION OF PVD AND CVD COATED HARDMETALS W. Kig, R. Fritsch (RWI’H Aachen, Aachen, Germany). ht. J. Refractory Metals Hard Mater., Vol 14, No l/3, 1996, 21-30. (In German.) Cutting performance of coated cemented carbides is discussed with regard to thickness and coating adhesion, effects of 48
MPR June 1996
temperature on properties of substrate, cutting speeds and tool life. It is reported that Ti basedarc-PVD coatings, deposited at 500°C improved cutting performance in interrupted turning of hardened and tempered steel, which requires high toughness in the tool. Machining of austenitic and stainless steel requires resistance to coating exfoliation. Comparison between PVD and CVD coated carbides shows the advantage of increased toughness accruing from reduced deposition temperature. COMPARISON OF STEEL-MILLING PERFORMANCE OF COATED CARBIDE INSERTS D.T. Quint0 et al. (Kennametal Inc, I&robe, Pennsylvania, USA). Znt. J. Refractory Metals Hard Mater., Vol 14, No l/3, 1996, 31-40. PVD-TiN, PVt-Ti (C,N) and CVDTi (C,N) deposited at moderate temperatures are compared. It is shown that cutting conditions and geometry determine optimum cutting performance. PVD coatings have a compressive residual stress which delays crack initiation. Where thermal shock is mild the performance of PVDTi(C,N) coated tools is maximized. CVD coatings require a strong cutting edge for maximization. Practical implications are discussed. DEVELOPMENT PRODUCTION AND APPLICATION OF NOVEL GRADES OF COATED HARDMETALS A. Anikeev et al. (Hard and Refractory Metals Research Inst., Moscow, Russia). lnt. J. Refiactorg Metals Hard Mate-r., Vol 14, No l/3, 1996, 41-48. A novel approach to development, and the introduction of new, coated hardmetals are reported. These combine toughness, durability and increased wear resistance which are attributed to fine scale microstructures developed through new technology. WEAR CHARACTERISTICS AND PERFORMANCE OF CVD ALUMINAZIRCONIA COMPOSITE COATINGS W.C. Russell, C. Strandberg. (Valenite Inc, Troy, Michigan, USA). ht. J. Refiuctory Metals Hard Mater., Vol 13, No l/3, 1996, 51-58. The development of CVD AlaOs-ZrOa coatings of cemented carbide tools is reported. The structure is substrate/ Ti (C,N) /A120s/AlzOs- (30 to 40) %ZrOz and this was used to analyze wear. The coating was found to be most effective when failure is driven by temperature and chemical diffusion. The coating impedes heat transfer to the substrate, reducing cracking, and reduces crystal growth during CVD and gives a smoother deposit.
RESISTANCE AU FROTTEMENT SEVERE DE COMPOSITES METALLIQUES A PARTICULES L. Scheed et al. (Ecole de Technologie Superieure, HenriJulien, Montreal, Quebec, Canada). Canadian Metall. Quart., Vol 34, No 3, 1995, 363-371. (In French.) An investigation of severe wear of SIC reinforced materials is described. Wear behaviour and mechanisms were studied with respect to rubbing speed, applied load and vol%SiC. Two wear thresholds are identified. It is shown that the particles protect the composite against wear while the temperature increase, caused by friction, does not affect the mechanical properties of the matrix. FABRICATION OF METAL MATRIX COMPOSITES USING COATED FILLERS BY POWDER METALLURGY P. Yih, D.D.L. Chung (State University of New York, Buffalo, New York, USA). ht. J. PowderMetall., Vol31, No 4, 1995, 335-340. It is reported that improved properties arise from use of coated fillers in making metal matrix composites. These include lower porosity, higher hardness and compressive strength, lower thermal and lower thermal and expansion, electrical conductivity. The coatings are thought to prevent filler/filler contact and to aid uniform distribution of the tiller in the matrix which enhances sintering and densification. CRACKING OF SILICON CARBIDE IN PM PROCESSED ALUMINIUM MATRIX COMPOSITE MATERIALS B. Wang et al. (University of Alabama, Birmingham, Alabama, USA). Metall. Muter. Trans. A, Vol 26A No 9, 1995, 2457. 2467. A study of Sic particle fracture during deformation of liquid phase sintered Al alloy matrix composites, containing 9vol% of 23, 63 or 142pm particles Sic, is described. The amount of surface area created by cracking and the number of cracked particles were determined. The factors are reported to depend on local strain and the condition of the matrix. The number of cracked particles was larger in the specimens with larger particles or higher matrix strength. The results are discussed.
Hard materials and tool steels EFFECT OF OXIDATION OF SILICON NITRIDE POWDER ON MECHANICAL PROPERTIES AND STRUCTURE T. Yanai, K. Ishizaki. (Nagaoka University of