Densification of nickel-carbide composites

Densification of nickel-carbide composites

model shows that changes of considerable magnitude occur in the stress components normal to the applied load and that in a real m a t e r i a l with a...

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model shows that changes of considerable magnitude occur in the stress components normal to the applied load and that in a real m a t e r i a l with a viscoelastic matrix that certain stresses could increase markedly with time. It is proposed that the alteration of stresses with time be given more consideration in the design of composite materials in the future. (71[1/107)

CERAMIC MATRICES Hot pressing and mechanical properties of AI20s with an Mo dispersed phase Rankin, D. T., Stiglich, J. j., Petrak, D. R. and Ruh, R. Jour.nal o/ the

American Ceramic Society, Vol 54, No 6, p 277 (June I971) Composites of up to 5vo1% molybdenum in alumina were made by hot pressing when. nearly theoretical densities were achieved. Molybdenum additions were found not "to affect grain growth of the alumina neither to affect the tensile strength but to reduce the elastic moduli and micro-hardness. T h e tensile strength of these composites was found to be dependent on grain size but the fracture energy of a l u m i n a / 5 v o l % molybdenum was 50% greater than that of alumina alone. (71/2/8) The influence of fibrous aluminium nitride on the strength of sintered A1N-Y~O, Komeya, K. and Inoue, H. Trans-

actions and Journal of the. British Ceramic Society, Vol 70, No 3, pp I07-113 (I971) T h e system A1N-Y20~ was studied with a view to developing a structural material of high strength. Sintering at 1400°C or above led to the formation of two crystal phases YsA150,~ and AI,Y,Og. Specimens with below 25% Y2Os and sintered above 1700°C contained a third, fibrous phase provisionally identified as A1N. Although high densities were achieved in specimens containing above 30% Y,Os the strengths were comparatively low and the structure was not fibrous. T h e highest strengths (flexural) were a r o u n d 0.35 G N / m ' . (71/2/9) Some properties of polymer impregnated cements and concretes Auskern, A. and Horn, W. Journal of

the American Ceramic Society, Vol 54, No 6, p 282 (June 197I) Polymer impregnation of cement and concrete was achieved by vacuum filling cured and dried cement and concrete with m o n o m e r . a n d subsequently polymerizing this by thermal catalysis or gamma radiation. Significant increases in strength of concrete were noted as a result of polymer impregnation and an empirical model is presented to enable a strength increase due to impregnation to be predicted. This composite material model considers both increased strength in the cement phase as well as improved b o n d i n g between the cement and aggregate. (71 / 2 / 10)

METAL MATRICES A barrier coating on tungsten fibers for nickel-base reinforced composites Frantsevich, I. N. et al, Soviet Powder

Metallurgy and Metal Ceramics, No 10, pp 813-817 (October 1970) A technique was developed for forming a layer of WAIl= on to tungsten fbres by vacuum deposition. T h e coated fibres were introduced into a nickel matrix by a vacuum-diffusion welding process and found to remain stable with respect to the nickel for not less than 100 hours at 1200°C. (71/3/32) Behavior of boron nitride and aluminium nitride particles in a molybdenum matrix Alfintseva, R. A. Soviet Powder

Metallurgy and Metal Ceramics, Vol 10, No 1 (97), p 65 (January 1971) Composites of up to 8 vol% nitride in molybdenum were made by hot pressing at 1600°C and examined metallographically and by means of micro-hardness. From these investigations it was concluded that dispersed boron nitride particles are unstable in molybdenum at 1600°C but that a l u m i n i u m nitride particles are stable up to 1800°C and appear to form no new phase at this temperature. (71/3/33) Correlation of creep elongation and substructure in alumiuium/stainless-steel composites Pinnel, M . R. and Lawley, A.

Metallurgical Transactions, Vol 2, No 5, pp 1415-1422 (May 1971) T h e tensile creep behaviour of a l u m i n i u m reinforced with up to 0-33 volume fraction of stainless steel wire was investigated. T h e reinforcement was found to reduce the creep rate at a given stress significantly. At all volume fractions of reinforcement, steady-state-creep conditions were attained a n d the steady-state-creep rates agreed well with those predicted by an exponential form of the ruleof-mixtures. Observation of the dislocation substructures in thin foils by electron microscopy revealed that the deformation in the matrix was independent of distance from the fibre/ m a t r i x interface. (71 •3•34) Deformation and fracture in A l - e u ~ eutectie composites Pattnaik, A. and Lawley, A. Metal-

lurgical Transactions, Vol 2, No 6, pp 1529-1536 (June 1971) Directional solidification of the Cu-A1 eutectic was used to produce a composite of aligned CuA1, lamellae with a spacing of 2 ~ m or less in an AI matrix. T h e composite was tested in compression along m e axis of lamellar growth and it was found that the yield stress in compression is higher than in tension. This was attributed to thermally-induced residual stresses. A high yield stress of the aluminium matrix was attrib~tted to constraints caused by the fine tamellar spacing and this was

supported by observations of the deformation substructure using electron microscopy. Failure of the composite was brought about by buckling and cleavage of the CuAL lamellae. (71 / 3 / 35) Densification of nickel-carbide composites Boiko, P. A. and Scherban, N. I.

Sovidt Powder MetaUurgy and Metal Ceramics, No 10, pp 802-804 (October 1970) A study was made of the effect of up to 16 vol% additions of ZrC, NbC and W C on the compacting behaviour of Ni powder. It was found that pressed density of the powder at a given .compacting pressure decreased with increasing carbide content. (71 / 3 / 36) Dilation des materiaux composites borealuminium (in Frcr~h) Ferte, J. P. and Villamayor, M.

Fibre Science and Technology, Vol 4, No l, p 49 (July 1971) T h i s p a p e r concerns the thermoplastic behaviour of unidirectionally reinforced composites of boron in a l u m i n i u m a n d some of its alloys when these materials are subjected to considerable changes of temperature. A mathematical relationship is used to obtain the number o f heating cycles that such materials can withstand before matrix cracking occurs. An abstract in English is provided. (71/3/37) Elec~ronlngnetic properties of euteetie composites (a critical review) Weiss, H. Metallurgical Transactions,

Vol 2, No 6, pp 1513-1521 (June 1971) T h e .electromagnetic properties of eutectlc composites are described for the cases of a metallic, a semiconducting o r an insulating matrix. It is concluded that the aligned eutectic, InSb-NiSb, is the only known composite which has suitable properties for magnetorresistive devices. (71/3/38) Fiber strengthening of a Cu-Fe-Cr duplex alloy by cold drawing Masaharu, Yamaguchi, et al, Metal-

lurgical Transactions, Vol 2, No 5, pp 1293-1296 (May 1971) An aligned-fibre composite ,~a~, produced by cold drawing wires of a copper alloy which contained about 25 vol% of a chromium ferrite phase. T h e wires were subsequently annealed at 480°C. T h e chromium ferrite occurred as needles. Wire with a diameter of 3 mm exhibited tensile strengths of up to 5 0 k g f / m m ' and elongations of up to 8%. F u r t h e r drawing of tile annealed alloy further increased the strength. (71/3/39) Magnetic properties of Co-Nb and Co-Nb-Fe unidirectioually solidified eutectie composites Coiling, D. A. and Kossowsky, R.

Metallurgical Transactions, Vol 2, No 6, pp 1523-1527 (June 1971) Unidirectional solidification was used to produce composites of aligned lamellae of NbCo~ in a matrix of a cobalt rich alloy, by solidifying Co-Nb

COMPOSITES December 1971