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Particle distribution control in cast aluminium alloy-mica composites
w h i s k e r , m a t r i x intcrfacial bond and hence increascs lhc tensile slrenglh of lhc composite.
METAL MATRICES Cast aluminium alloy-mica composite Gupta, A.K., Dan, T.K., Rohatgi, P.K. and N at h, D. Journal ql'MateriaL~ Science Letler~ l'ol 6 No 1 (Januao, 1987) pp 3.5-37 A method is described for the fabrication of a composite containing a dispersion of 2.5 wt% uncoated mica particles in an aluminium alloy matrix. The addition of 1 wt% Mg was found to improved lhe wcllabilit~ of the mica particles and aid dispersion. The disiribution of mica particles in thc casting was examined using optical lind scanning eleclron microscopy. showing a fairly unilk)rnl dislribution but ,,',ittl some conglomeration duc 1o segregation of mica particles of diffcrcnl sizes and shapes. X-ray analysis across a mica parlicle showed segregation of magnesium and silicon ill the mica/malrix inlcrface. Poor interfacial bonding leads IO a decrease in slrenglh compared ~ith lhc pure matrix material bul enhances the lubricating propcrtics o f the comp(/site. Effect of dispersed graphite on the freezing rate of gravity, die-cast LMI3 alloy-3 wt% graphite particle composite lha, A.K.. Asthana. R.. l)ao. T.K. and Roh atgi, P.K. Journal q/'Mat('riaLv Sci('n((" Lctt('r~ l'ol 6 No 2 (F(,hruary 1987) pp 225-228 Additions of graphite ill castings arc found to dccreasc the cooling rate of graphite particle/ ahlminium alh)y composilcs castings compared with the pure alloy since the graphite parlicles obstruct thc heat I]ow fronl lhe bulk metal. The cooling ralc was analysed using microscopic nleasurcnlents of dendritic arm spacing. A parliclc-frec zonc ncar Ihc boIlom of the casting arises due to l]otation of the graphite particles which arc frozen in posilion when they meet the advancing solidification front. The ]mmogcneity of the particle distribution was analysed by determining the profile of lhc parlicle-free zone lk)r differcnl graphile particle sizes. Fahrication of multi-lamina metallic glass/ aluminium composites by' explosive compaction Friend, CM. and McKenzie, P.J. Journal qf Materials Sciencc l,(,tt(,rs I;';/6 No 1 (,lanua O' 1(.'8'7) pp 103-105 Optimum conditions lbr the explosive compaction of metallic glass/aluminium composites were determined, and the condition of the matrix and reinforcing phases wlts assessed after fabrication. The interfacial bond between the metallic glass and the aluminium was found to be physical rather than chemical. X-ray diffraction shows that the metallic glass remains amorphous, indicating that the maximum tempcrature reached during compaction is low enough not to cause it to recrystallize: the matrix becomes less work hardened and recovers. Hence, composites may be fabricated using this technique with minimal damage to the reinforcement or reaction between the phases. Flame-spraying fabrication of silicon carbide whisker-reinforced aluminium ]sunekawa. Y., Okumiya, M.. Niimi. I. iuld O k u m u r a. K. Jou rn a I o/'Ma terials S('ien ('(, L(,tt(,r~ Vol 6 No 2 (Febnmn, 1987) pp 191-193 The porosity and whisker distribution and orientation in flame-sprayed silicon carbMe whisker/aluminium composites has been determined using various techniques. Both the as-fabricated pre-lorms and material l\)rged at different temperatures were examined and their tensile mechanical properties measured. An increase in forging temperature enhances the
COMPOSITES
. JULY
1987
Interaction of AI-Si, AI-Ge and Zn-AI entectic alloys with SiC/AI discontinuously reinforced metal matrix composites Moshier, W.C., Ahearn, J.S. and Cooke. D.C. Join'rod ql'Mawriat~ Sch'me 17)122 .Vo l (Jamtari 1987) pp 115-122 The interactions occurring bctv, een S i ( A I composites and the cutcclic alloys AI-Si. AI-Ge and Zn-A1 are examhlccl. The Z n - : \ l alloy was ibuud to penetrate the composite Io a limited extent (50 gill) ~llld reaction bel'Aecn tile lille) ilud the cc)mposite ',',as slow. The Al-Si and AI-Ge alloys showed a greater penetration (sc',eral millimctres) into the composite. The processing history' of the conlpositc v, as found to inlluence the reaction between alloy and composite, reaclion being strongest in composites that had been worked (extruded and cross-rolled). The differences in interaction between the alloys and composite is explained b) considering the microslrucmrc ot" the composite and the abilit~ of the alloy to ,act the SiC fibres.
Particle distribution control in cast aluminium alloy-mica composites Nath, D.. Asthana, R. and Rohatgi. PK.Journal ql' Material.s Sciem'e l"ol 22 No 1 (Ju#IHU0 10,~7) pp 170-176 The effects of heat flow on the distribution o f mica particles in the solidification of an AI-4 wt% ('u-15 wt% Mg alloy containing a suspension of mica particles ~ a a s studied. Movement of the particles during solidificalion results in segregation oflhc particles which is a resuh of Ihc l]otation of mica particles in the aluminiuna alloy. The deviation of particle distribution from that predicted by Stoke's law and freezing-time calculations nlay bc due to the pariial welting o f the particles b,,, tlic liquid allot. Methods which could reduce particle segrcgalion are discussed.
Thermal residual stress in metal matrix composite Arsenault, R.J. and Taya. M. Acta Metallur~ica. Vol 35 No 3 (1987) pp 651-659 The residual thermal stresses in a short whisker metal matrix composite (silicon carbide whiskers in 6061 aluminium alloyl and its cflL'ci on the yield stress of this material were studied. Comparisons between the observed ditfercnces in compressive and tensile yield stresses were made with those predicted from a theoretical model based on Eshelby's method and agreement v, as found to be vc W good. Wetting of solids by molten metals and its relationship to the preparation of metal matrix composites Delanna), F.. Froyen. L. and Deruyttere, A. Journal o/'Material~ Scium'e 1o/22 No 1 (Jamtary 198D pp 1-16 This revic,a links the fundamental concepts of wetting to current liquid metal infiltration lechniques in metal matrix compositcs. The general thermodyimmic principles ot wetting and the effects of non-equilibrium conditions Iound at the liquid-solid interface are discussed. Wetting between liquid and solid metals is co'~ered. Techniques used to enhance wetting in practical metal matrix systems arc discussed. Particular attention is paid to reinforcements made of carbon, silicon carbide and alumina and the effects of surface treatments and/or coatings on these fibres, and also tile cl'I;ects o f alloying additions to the metal matrix.
ORGANIC FIBRES Effect of fibre volume fraction on the strength of Kevlar-29/epoxy strands Weinberg. A. and Sch~artz, P. Jounla/ o~ Alaterial~ &'Junco Lem,rv 101 6 ,%,7~2 H';'hrmln 1987) pp 183-184 Strands of Ke,,lar-29 fibres v, erc impregnated ,aith epoxy resin to gixe samples of different 1"I and then tested in tension. ]'he tensile strength x~,as found to be relatixcl} independent of 1"l up to ~- (~(t-65%, then falls l,,) the strength of the uninlprcgnaled yarn at higher I'ibre content. A difference in failure nlode with l t x~as obsep, ed. The presence of resin-poor arcil'~ ilia} decrease the strength b} allotting fibrc misalignment and by increasing thc inel'fectix c fibre length ill high 1"I.
RESIN MA TRICES Acoustic emission monitoring of stress corrosion cracks in aligned GRP Ku mosa, M Jourmd otlflu ~ic.~ D: tl,tUicd Phy,~ic~ l'ol 20 No 1 (1987) pp 69-74 ]'he acoustic emission produced by the grm~th of a stress corrosion crack through an aligned glass-reinlorccd pobester resin was studied. In this mode of faihlre, crack gro'a th is planar 'Mth little or no fibre pull-out or dcbondmg. The rcstdts shov, thai a log-nornla] distribution git,cs a rcasonabl} close approximation to the experimental amplitude distribution of signals produced b,, fibre/fibre fracture in planar stress corrosion cracking. Deviations from this beha',tour arc caused by debonding mid fibre pullout phcnonlcn~l.
Acoustic emission from stress corrosion cracks in aligned GRP Kunlosil, M., Hull, l). and Price. J.N. Journal oI' MawriaZ~ Scicm'u l'ol 22 ,V. 1 (I~,',~D pp 331-336 "lhe acoustic emission ,(AE)fronl a glass-fibre/ polyester unidirectional laminate undergoing stress corrosion cracking was measured. ('rack growlh tinder these conditions was found to be controlled, with tile only source of AE being fibre frilcture. A one-to-one relationship ~vas lound between tile numbcr o f fibre failures and thc number of high amplitude signals detected. Also tile amplitude of the signals prodnced by fibre faihlre was lottnd to be proportional to the applied stress intensit?. Ashestns-brucile-polyphenylene snlphide composites. Part I: Chemical and electrochemical degradation in hot alkali Montoneri, E.. Modica. G. and Ma fl], S.Journal of Uomposiw Materiah l Td 20 (Nm'ember 1986) pp 504-519 The chcnlical and electrochemical degradation of cry'settle asbestos composites contaioing 11-47% polyphenylenc sulphidc {PPS) was studied and the results compared to those of asbestos-PPS-Mg(OH), and asbestos-Mg(OH) 2 composites. Chemical ageing (2500 h in boiling 31)% KOH) and electrochemical ageing (660-3528 h under electrolysis at IA cm --~ in 90-12()~C, 40-50% KOII) were perlormed. IR spectroscop~ was u s d to determine local PPS, asbestos lind brucitc contents. It ',~,as l()tllld that asbestos-PPS composites are 2.5-SS thnes more stable than plain asbeslos or asbcstos-brucilc composites. Asbestos hydrolysis occuring over unprotected fibres is the main cause ol'malcrial loss. Under electrolysis mechanical erosion dominates, and ~(I zero electrode gap the mininmm load ,,)1" PPS for satisfactory perlbrnmncc is 2~)",.
265
METAL MATRICES Cast aluminium alloy-mica composite Gupta, A.K., Dan, T.K., Rohatgi, P.K. and N at h, D. Journal ql'MateriaL~ Science Letler~ l'ol 6 No 1 (Januao, 1987) pp 3.5-37 A method is described for the fabrication of a composite containing a dispersion of 2.5 wt% uncoated mica particles in an aluminium alloy matrix. The addition of 1 wt% Mg was found to improved lhe wcllabilit~ of the mica particles and aid dispersion. The disiribution of mica particles in thc casting was examined using optical lind scanning eleclron microscopy. showing a fairly unilk)rnl dislribution but ,,',ittl some conglomeration duc 1o segregation of mica particles of diffcrcnl sizes and shapes. X-ray analysis across a mica parlicle showed segregation of magnesium and silicon ill the mica/malrix inlcrface. Poor interfacial bonding leads IO a decrease in slrenglh compared ~ith lhc pure matrix material bul enhances the lubricating propcrtics o f the comp(/site. Effect of dispersed graphite on the freezing rate of gravity, die-cast LMI3 alloy-3 wt% graphite particle composite lha, A.K.. Asthana. R.. l)ao. T.K. and Roh atgi, P.K. Journal q/'Mat('riaLv Sci('n((" Lctt('r~ l'ol 6 No 2 (F(,hruary 1987) pp 225-228 Additions of graphite ill castings arc found to dccreasc the cooling rate of graphite particle/ ahlminium alh)y composilcs castings compared with the pure alloy since the graphite parlicles obstruct thc heat I]ow fronl lhe bulk metal. The cooling ralc was analysed using microscopic nleasurcnlents of dendritic arm spacing. A parliclc-frec zonc ncar Ihc boIlom of the casting arises due to l]otation of the graphite particles which arc frozen in posilion when they meet the advancing solidification front. The ]mmogcneity of the particle distribution was analysed by determining the profile of lhc parlicle-free zone lk)r differcnl graphile particle sizes. Fahrication of multi-lamina metallic glass/ aluminium composites by' explosive compaction Friend, CM. and McKenzie, P.J. Journal qf Materials Sciencc l,(,tt(,rs I;';/6 No 1 (,lanua O' 1(.'8'7) pp 103-105 Optimum conditions lbr the explosive compaction of metallic glass/aluminium composites were determined, and the condition of the matrix and reinforcing phases wlts assessed after fabrication. The interfacial bond between the metallic glass and the aluminium was found to be physical rather than chemical. X-ray diffraction shows that the metallic glass remains amorphous, indicating that the maximum tempcrature reached during compaction is low enough not to cause it to recrystallize: the matrix becomes less work hardened and recovers. Hence, composites may be fabricated using this technique with minimal damage to the reinforcement or reaction between the phases. Flame-spraying fabrication of silicon carbide whisker-reinforced aluminium ]sunekawa. Y., Okumiya, M.. Niimi. I. iuld O k u m u r a. K. Jou rn a I o/'Ma terials S('ien ('(, L(,tt(,r~ Vol 6 No 2 (Febnmn, 1987) pp 191-193 The porosity and whisker distribution and orientation in flame-sprayed silicon carbMe whisker/aluminium composites has been determined using various techniques. Both the as-fabricated pre-lorms and material l\)rged at different temperatures were examined and their tensile mechanical properties measured. An increase in forging temperature enhances the
COMPOSITES
. JULY
1987
Interaction of AI-Si, AI-Ge and Zn-AI entectic alloys with SiC/AI discontinuously reinforced metal matrix composites Moshier, W.C., Ahearn, J.S. and Cooke. D.C. Join'rod ql'Mawriat~ Sch'me 17)122 .Vo l (Jamtari 1987) pp 115-122 The interactions occurring bctv, een S i ( A I composites and the cutcclic alloys AI-Si. AI-Ge and Zn-A1 are examhlccl. The Z n - : \ l alloy was ibuud to penetrate the composite Io a limited extent (50 gill) ~llld reaction bel'Aecn tile lille) ilud the cc)mposite ',',as slow. The Al-Si and AI-Ge alloys showed a greater penetration (sc',eral millimctres) into the composite. The processing history' of the conlpositc v, as found to inlluence the reaction between alloy and composite, reaclion being strongest in composites that had been worked (extruded and cross-rolled). The differences in interaction between the alloys and composite is explained b) considering the microslrucmrc ot" the composite and the abilit~ of the alloy to ,act the SiC fibres.
Particle distribution control in cast aluminium alloy-mica composites Nath, D.. Asthana, R. and Rohatgi. PK.Journal ql' Material.s Sciem'e l"ol 22 No 1 (Ju#IHU0 10,~7) pp 170-176 The effects of heat flow on the distribution o f mica particles in the solidification of an AI-4 wt% ('u-15 wt% Mg alloy containing a suspension of mica particles ~ a a s studied. Movement of the particles during solidificalion results in segregation oflhc particles which is a resuh of Ihc l]otation of mica particles in the aluminiuna alloy. The deviation of particle distribution from that predicted by Stoke's law and freezing-time calculations nlay bc due to the pariial welting o f the particles b,,, tlic liquid allot. Methods which could reduce particle segrcgalion are discussed.
Thermal residual stress in metal matrix composite Arsenault, R.J. and Taya. M. Acta Metallur~ica. Vol 35 No 3 (1987) pp 651-659 The residual thermal stresses in a short whisker metal matrix composite (silicon carbide whiskers in 6061 aluminium alloyl and its cflL'ci on the yield stress of this material were studied. Comparisons between the observed ditfercnces in compressive and tensile yield stresses were made with those predicted from a theoretical model based on Eshelby's method and agreement v, as found to be vc W good. Wetting of solids by molten metals and its relationship to the preparation of metal matrix composites Delanna), F.. Froyen. L. and Deruyttere, A. Journal o/'Material~ Scium'e 1o/22 No 1 (Jamtary 198D pp 1-16 This revic,a links the fundamental concepts of wetting to current liquid metal infiltration lechniques in metal matrix compositcs. The general thermodyimmic principles ot wetting and the effects of non-equilibrium conditions Iound at the liquid-solid interface are discussed. Wetting between liquid and solid metals is co'~ered. Techniques used to enhance wetting in practical metal matrix systems arc discussed. Particular attention is paid to reinforcements made of carbon, silicon carbide and alumina and the effects of surface treatments and/or coatings on these fibres, and also tile cl'I;ects o f alloying additions to the metal matrix.
ORGANIC FIBRES Effect of fibre volume fraction on the strength of Kevlar-29/epoxy strands Weinberg. A. and Sch~artz, P. Jounla/ o~ Alaterial~ &'Junco Lem,rv 101 6 ,%,7~2 H';'hrmln 1987) pp 183-184 Strands of Ke,,lar-29 fibres v, erc impregnated ,aith epoxy resin to gixe samples of different 1"I and then tested in tension. ]'he tensile strength x~,as found to be relatixcl} independent of 1"l up to ~- (~(t-65%, then falls l,,) the strength of the uninlprcgnaled yarn at higher I'ibre content. A difference in failure nlode with l t x~as obsep, ed. The presence of resin-poor arcil'~ ilia} decrease the strength b} allotting fibrc misalignment and by increasing thc inel'fectix c fibre length ill high 1"I.
RESIN MA TRICES Acoustic emission monitoring of stress corrosion cracks in aligned GRP Ku mosa, M Jourmd otlflu ~ic.~ D: tl,tUicd Phy,~ic~ l'ol 20 No 1 (1987) pp 69-74 ]'he acoustic emission produced by the grm~th of a stress corrosion crack through an aligned glass-reinlorccd pobester resin was studied. In this mode of faihlre, crack gro'a th is planar 'Mth little or no fibre pull-out or dcbondmg. The rcstdts shov, thai a log-nornla] distribution git,cs a rcasonabl} close approximation to the experimental amplitude distribution of signals produced b,, fibre/fibre fracture in planar stress corrosion cracking. Deviations from this beha',tour arc caused by debonding mid fibre pullout phcnonlcn~l.
Acoustic emission from stress corrosion cracks in aligned GRP Kunlosil, M., Hull, l). and Price. J.N. Journal oI' MawriaZ~ Scicm'u l'ol 22 ,V. 1 (I~,',~D pp 331-336 "lhe acoustic emission ,(AE)fronl a glass-fibre/ polyester unidirectional laminate undergoing stress corrosion cracking was measured. ('rack growlh tinder these conditions was found to be controlled, with tile only source of AE being fibre frilcture. A one-to-one relationship ~vas lound between tile numbcr o f fibre failures and thc number of high amplitude signals detected. Also tile amplitude of the signals prodnced by fibre faihlre was lottnd to be proportional to the applied stress intensit?. Ashestns-brucile-polyphenylene snlphide composites. Part I: Chemical and electrochemical degradation in hot alkali Montoneri, E.. Modica. G. and Ma fl], S.Journal of Uomposiw Materiah l Td 20 (Nm'ember 1986) pp 504-519 The chcnlical and electrochemical degradation of cry'settle asbestos composites contaioing 11-47% polyphenylenc sulphidc {PPS) was studied and the results compared to those of asbestos-PPS-Mg(OH), and asbestos-Mg(OH) 2 composites. Chemical ageing (2500 h in boiling 31)% KOH) and electrochemical ageing (660-3528 h under electrolysis at IA cm --~ in 90-12()~C, 40-50% KOII) were perlormed. IR spectroscop~ was u s d to determine local PPS, asbestos lind brucitc contents. It ',~,as l()tllld that asbestos-PPS composites are 2.5-SS thnes more stable than plain asbeslos or asbcstos-brucilc composites. Asbestos hydrolysis occuring over unprotected fibres is the main cause ol'malcrial loss. Under electrolysis mechanical erosion dominates, and ~(I zero electrode gap the mininmm load ,,)1" PPS for satisfactory perlbrnmncc is 2~)",.
265