1. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Thermal Expansion Behaviour of Metal-Matrix Composites T. Huber, A. Mohammed and H.P. Degischer Vienna University of Technology Institute of Materials Science & Testing, A-1040 Vienna/Austria

2. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Part I Thermal Expansion Behaviour of Particle Reinforced Metal-Matrix Composites

3. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Metal Matrix Composites Studied – Particle Reinforced Material P2 (P1 is similar) Material Code MatrixReinforcement Fabrication process Condition P1Al99.5 SiC p ; 70 vol.-% particle size: 3 m to 80 m gas pressure infiltration as-cast P2 AlSi7Mg (A356) overaged P3 AlSi7Mg (A356) SiC p ; 55 vol.-% particle size: ~80 m centrifugal casting overaged P4 AlSi10Mg (A359) SiC p ; 20 vol.-% particle size: ~12 m stir casting/ extruded overaged Material P3Material P4

4. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Thermal Mechanical Analysis (TMA) TA Instruments ® TMA 2940 (Wilmington, Delaware) Percent Length Change (PLC) Instantaneous Coefficient of Thermal Expansion (CTE) (from 50°C to 490°C) 500°C RT Calculated parameters:

5. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Thermal Expansion Behaviour of AlSiC MMC Section III Section I Section II thermal behavior depends strongly on the reinforcement architecture material P2: Si-bridges between SiC particles forming a percolating SiC-Si-network … … prevent an accelerated thermal expansion linear to decreasing L/L 0 (T) internal stresses in the matrix surpass decreasing yield strength … … relaxation processes (plastic flow, creep) occur reduction in thermal expansion vanishing internal stresses non linear increase of L/L 0 (T) with significant elastic straining Youngs modulus decreases with temperature

6. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Thermal Expansion Behavior of AlSiC MMC Section II Section III Section I non linear increase of L/L 0 (T) increasing CTEs (slope of L/L 0 curve) significant elastic straining of the matrix linear to decreasing L/L 0 (T) CTE reaches a maximum and drops thermal expansion is more and more dominated by the densely packed ceramic simultaneously: closure of microvoids by local plastic flow of the matrix may occur material P2: Si-bridges between SiC particles forming a percolating SiC-Si-network … … prevent an accelerated thermal expansion constant CTEs up to 500°C material P1: matrix is continuously expanding (non percolating reinforcement) increasing CTE & voids being already filled with metal matrix

7. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Microstructure of Al-SiC MMC – Material P2 (Section II & III) thermal behavior in section III depends strongly on the reinforcement architecture material 1 & 3: Si-bridges between SiC particles forming a percolating SiC-Si-network … … prevent an accelerated thermal expansion SiC Si

8. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Big SiC particles surrounded by small SiC particles connected via Si-bridges from the matrix alloy. Compact cluster of SiC particles connected via Si-bridges. after dendritic solidification of the matrix alloy ( -phase) remaining eutectic liquid (12.6 mass-% Si) tends to freeze around the SiC particulates ceramic particles do not act as preferential crystal nucleation sites Si-bridges between SiC particles form a percolating SiC-Si-network Microstructure of Al-SiC MMC – Material P2 (Section II & III)

9. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Preexisting Microvoids – Material P2 (Section II & III) voids (a) SEM backscattered electron image (BEI) (b) Image analysis – binary image of (a) (white area = voids) Overlay of (a) and (b) average void volume fraction of an AlSiC MMC (result of 12 images) 1.3 0.5 vol.-% Uncertainties of measurement: broken SiC particles and removal of matrix alloy during metallographic preparation overestimation closure of pores by smearing during metallographic preparation underestimation of porosity

10. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Expansion Behaviour of the Matrix (Section II & III) SEM micrograph of partially dissolved A356 alloy (removal of solid solution) showing the eutectically segregated Si-network pure Al increasing CTEs A356 alloy - cast similar behaviour as P1 and P2 percolating Si-network A356 alloy – cold rolled destroyed Si-network no CTE drop down occurs

11. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Expansion Behaviour of different Particle Reinforced MMCs Al99.5 matrix -phase (eutec.) Si AlSi7Mg or AlSi7 matrix: Material P1 Material P2 SiC -phase (eutec.) Si AlSi7Mg or AlSi7 matrix: Material P3

12. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Expansion Behaviour of an Extruded MMC Extruded material destroyed Si-network no CTE drop down occurs

13. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Solution treatment 530°C / 6h Quenched in water Slow cooling with 3K/min Temp. Time RT Influence of Heat Treatments on the thermal behaviour – Material P2 Heat treatment 400°C / 30 min Quenched in water

14. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Peak within 1 st heating up cycle Gradual formation of equilibrium phase Mg 2 Si precipitates (incoherent, overaged) in the A356 alloy, which causes a small additional volume change! Influence of Heat Treatments on the thermal behaviour – Material P2 Coherent precipitate Incoherent precipitate L Formation of incoherent Mg 2 Si precipitates 70% of L Formation of incoherent Mg 2 Si precipitates 70% of L relief of internal stresses from quenching 30% of L

15. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Conclusions – Particle Reinforced MMC CTE curves of P1 & P2 up to 500°C can be divided into three sections: section I: matrix with significant elastic straining section II: elastic straining decreases owing to decreasing yield strength of the matrix internal stresses can at least partly relax by local plastic flow section III: behavior depends on reinforcement architecture Al99.5 matrix: CTE increases again AlSi7Mg matrix: Si-bridges between SiC forming a SiC-Si-network prevent an accelerated expansion Eutectically segregated Si in an Al alloy (e.g. A356) forms a percolating Si network Thermal behaviour of the as-cast alloy is similar to the composite P2 Destruction of the Si network (plastic deformation), lead to a thermal behaviour like matrix with insulated reinforcement (increasing CTEs with rising temperature) These observations on the unreinforced matrix alloy verify the effect of the percolating SiC-Si-network on the thermal expansion of the composite P2 Solution quenched samples of Al-matrix-composites lead to a small additional expansion during a slow 1 st heating up cycle, due to formation of overaged incoherent Mg 2 Si precipitates in the AlSi7Mg matrix alloy & relief of internal stresses from quenching.

16. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Part II Thermal Expansion Behaviour of Fiber Reinforced Metal-Matrix Composites

17. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 CFR-MMCs Material MatrixPan C-FibersVol.Fr.%system AlMg0.2T300J65Woven 50% warp Bundle vol.fr. 70% AlMg0.2T300J65Woven 80% warp Bundle vol.fr. 70% Al99.8M40B74Unidirectional MgAl0.6M4070Unidirectional Mg99.8 Tenax HTA 5331 60Unidirectional Processing Gas pressure infiltration

18. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Experimental Procedure for CFR-MMCs Load 0.5N Rate 3K/min 2cycles -40 to 120°C 2cycles -40 to 200°C Time temperature cycles For micromechanical analysis

19. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Microstructure of CFR-MMCs MgAl0.2/C-T300J/65f (0/90°,50/50%), in- plane section MgAl0.2/C-T300J/65f (0/90°,50/50%), cross- section MgAl0.2/C-T300J/65f (0/90°,80/20%), in-plane section MgAl0.2/C-T300J/65f (0/90°,80/20%), cross- section Al/C-M40B/74f, UD cross section

20. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Irreversible plastic deformation CFR-MMCs Thermal Stresses Temperature, °C dl/l % Reversible plastic deformation Width of hysteresis Residual stresses Elastic deformation T cr Al l C Fiber Matrix 0 Stresses during cooling

21. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Thermal Mechanical Analysis (TMA) for CFR-Mg MCs

22. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Thermal Mechanical Analysis (TMA) for CFR-Al MCs Al/M40B/74f

23. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Residual stresses after thermal cycling for CFR-MMCs

24. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Inst.CTE vs Thermal cycling

25. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Inst.CTE vs Temperature for CFR-Mg MCs

26. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Al/M40B/74f + Mg/M40B/70f Polar diagrams for inst.CTE vs orientation MgAl0.2/C-T300J/65f (0/90°,50/50%) MgAl0.2/C-T300J/65f (0/90°,80/20%)

27. T. Huber and A. Mohammed CompTest2003, Châlons-en-Champagne Jan. 2003 Conclusions During thermal cycling, all the CFRM exhibit hysteresis of length change between heating and cooling. The level of plastic deformation is represented by the hysteresis width. Total strain, width of hysteresis are strongly dependent on - the fiber properties - thermal history - fiber orientation and arrangement. Residual stresses causing macroscopic deformation are produced by cooling from above a certain critical temperature T cr, which depends strongly on the matrix properties at elevated temperatures. The plastic deformation and the residual stresses are reproduced by following temperature cycles for the same temperature range. Transverse fibers of more than 20% increase the longitudinal expansion; low expansion in longitudinal direction is compensated by high expansion transverse and out of plane respectively. Instantaneous coefficient of thermal expansion (CTE) is not material constant for MMC.