Editing Metal matrix composite (section)

== Effect on Mechanical Properties ==
The addition of ceramic particles in general increases the strength of the material while having a tradeoff on material ductility. For example, a Al-Al<sub>2</sub>O<sub>3</sub> composite can increase the yield strength of cast Al 6061 alloys from 105 to 120 MPa and increase the [[Young's modulus|young’s modulus]] from 70 to 95 GPa.<ref>{{Cite journal |last=Park |first=B. G. |last2=Crosky |first2=A. G. |last3=Hellier |first3=A. K. |date=2001-05-01 |title=Material characterisation and mechanical properties of Al2O3-Al metal matrix composites |url=https://doi.org/10.1023/A:1017921813503 |journal=Journal of Materials Science |language=en |volume=36 |issue=10 |pages=2417–2426 |doi=10.1023/A:1017921813503 |issn=1573-4803}}</ref> However, the composite had negative effects on the ductility decreasing it from 10% to 2%. Ultimately, the increase in elastic modulus is significant because the metals get the benefit of the higher [[Specific modulus|specific stiffness]] of ceramics while retaining some [[ductility]].<ref>{{Cite journal |last=Suh |first=Jin-Yoo |last2=Lee |first2=Young-Su |last3=Shim |first3=Jae-Hyeok |last4=Park |first4=Hoon Mo |date=January 2012 |title=Prediction of elastic properties of precipitation-hardened aluminum cast alloys |url=https://doi.org/10.1016/j.commatsci.2011.07.061 |journal=Computational Materials Science |volume=51 |issue=1 |pages=365–371 |doi=10.1016/j.commatsci.2011.07.061 |issn=0927-0256}}</ref><ref>{{Cite book |last=Ashby |first=Mike |title=Materials Selection in Mechanical Design |publisher=Butterworth-Heinemann: Amsterdam |year=2005 |edition=3rd}}</ref> Metal-matrix composites can also significantly increase the wear resistance and hardness of aluminum alloys. Al<sub>2</sub>O<sub>3</sub> particles were found to significantly increase the wear resistance of an Al-Si alloy, and SiO<sub>2</sub> particles increased the hardness of a Al-Mg alloy significantly.<ref>{{Cite journal |last=Megahed |first=M. |last2=Saber |first2=D. |last3=Agwa |first3=M. A. |date=2019-10-01 |title=Modeling of Wear Behavior of Al–Si/Al2O3 Metal Matrix Composites |url=https://doi.org/10.1134/S0031918X19100089 |journal=Physics of Metals and Metallography |language=en |volume=120 |issue=10 |pages=981–988 |doi=10.1134/S0031918X19100089 |issn=1555-6190}}</ref><ref>{{Cite journal |last=Bhatt |first=J. |last2=Balachander |first2=N. |last3=Shekher |first3=S. |last4=Karthikeyan |first4=R. |last5=Peshwe |first5=D.R. |last6=Murty |first6=B.S. |date=September 2012 |title=Synthesis of nanostructured Al–Mg–SiO2 metal matrix composites using high-energy ball milling and spark plasma sintering |url=https://doi.org/10.1016/j.jallcom.2011.12.062 |journal=Journal of Alloys and Compounds |volume=536 |pages=S35–S40 |doi=10.1016/j.jallcom.2011.12.062 |issn=0925-8388}}</ref> The application of this is in light, wear-resistant alloys for wear components such as [[piston]] liners in automobile engines. Current aluminum alloys are soft and often require hard, heavy cast iron liners which reduces the benefits of the lightweight aluminum engines. 

[[Fracture toughness]] of the composites is typically dominated by the metal phases; however, it can also be dominated by the ceramic phase or delamination depending on the material system.<ref>{{Cite journal |last=Agrawal |first=Parul |last2=Sun |first2=C.T. |date=July 2004 |title=Fracture in metal–ceramic composites |url=https://doi.org/10.1016/j.compscitech.2003.09.026 |journal=Composites Science and Technology |volume=64 |issue=9 |pages=1167–1178 |doi=10.1016/j.compscitech.2003.09.026 |issn=0266-3538}}</ref> For example the Cu/Al<sub>2</sub>O<sub>3</sub> system has a high [[thermal expansion]] mismatch causing localized stresses encouraging crack propagation in the form of delamination. This significantly inhibits its fracture toughness compared to other compositions. In an Al/Al<sub>2</sub>O<sub>3</sub> co-continuous system the crack propagated through the ceramic phase and was deflected upon reaching interfaces with the metallic phases. As a result, more energy was needed to deflect the crack around the phases and the composite was significantly toughened. Overall, fracture toughness is largely dependent on MMC composition due to thermal mismatch and crack modes but can toughen composites with low thermal mismatch.

MMCs strengthen materials against [[Plasticity (physics)|plasticity]] for a variety of reasons. The first is direct load transfer to the stronger ceramic particles.<ref>{{Cite journal |last=Chawla |first=N. |last2=Shen |first2=Y.-L. |date=June 2001 |title=Mechanical Behavior of Particle Reinforced Metal Matrix Composites |url=https://onlinelibrary.wiley.com/doi/10.1002/1527-2648(200106)3:63.0.CO;2-I |journal=Advanced Engineering Materials |language=en |volume=3 |issue=6 |pages=357–370 |doi=10.1002/1527-2648(200106)3:6<357::AID-ADEM357>3.0.CO;2-I |issn=1438-1656}}</ref> The second is due to the difference in plastic deformation of the two components. This causes a [[dislocation]] to become pinned on the stronger particles and bow around them to continue moving. Dislocations typically drive plastic deformation due to the lower energy to move them rather than moving an entire plane of atoms. Therefore, pinning them causes a large increase in the energy and stress required for plastic deformation (see [[Precipitation hardening]]). The final mechanism is caused by the stress from thermal and coherency mismatch.<ref>{{Cite journal |last=Khraishi |first=Tariq A. |last2=Yan |first2=Lincan |last3=Shen |first3=Yu-Lin |date=June 2004 |title=Dynamic simulations of the interaction between dislocations and dilute particle concentrations in metal–matrix composites (MMCs) |url=https://doi.org/10.1016/j.ijplas.2003.10.003 |journal=International Journal of Plasticity |volume=20 |issue=6 |pages=1039–1057 |doi=10.1016/j.ijplas.2003.10.003 |issn=0749-6419}}</ref> This creates a stress field which traps dislocations creating a pileup further inhibiting plastic deformation.