D.C. Jia

Influence of SiC particulate size on the microstructural evolution and mechanical properties of Al-6Ti-6Nb matrix composites

Abstract Three kinds of SiC particulates (SiCp), whose diameters range from millimeter through micrometer to nanometer (designated as m-SiCp, μ-SiCp and n-SiCp, respectively), were separately incorporated into an Al–6wt.%Ti–6wt.%Nb alloy by high energy ball milling. The as-milled composite particles are appreciably refined particularly when finer SiC particulate was added, and so do the in situ formed Al 3 Ti, AlNb 2 dispersoids as well as the Nb particles. The room temperature strength and ductility of the composites, except for the stiffness, deteriorate unexpectedly. Nonetheless, elevated temperature strength and thermal stability of the composites are improved and greater strength over that of the Al–6Ti–6Nb matrix alloy is exhibited above 240°C. The changes of the mechanical properties from room to elevated temperature are correlated with the microstructure and fractographs.

Micro structure and mechanical properties of Al-12Ti-6Nb prepared by mechanical alloying

Abstract An alloy Al-12wt.% Ti-6wt.% Nb was prepared by mechanical alloying (MA) process and its microstructure, mechanical properties and thermal stability were investigated. It was shown that the MA Al-12Ti-6Nb is an Al matrix composite with uniformly distributed intermetallic Al 3 Ti dispersoids and single phase Nb flakes as well as fine equiaxed A1 2 O 3 and rod-shaped Al 4 C 3 phases. In most of the Al 3 Ti particles, especially the larger ones, island-shaped α-Ti cores are normally retained. After exposure at 550°C in air for 200 h, the Al 3 Ti dispersoids coarsen slowly and their α-Ti cores disappear, while the single phase Nb remains. Compared with the MA Al-12Ti fabricated in the same way, the MA Al-12Ti-6Nb shows much more excellent mechanical properties and thermal stability, which can be attributed to the more effective reinforcement of Al 3 Ti dispersoids and Nb flakes due to the alleviation of their thermal expansion mismatch with the Al matrix by the addition of Nb.

Molecular Dynamics Simulation of a Rigid Sphere Indenting a Copper Substrate

Three-dimensional molecular dynamics (MD) simulation is used to study the atomic-scale indentation process of a spherical diamond tip in contact with a copper substrate. In the indentation simulations, the force-displacement curve is obtained and compared with a modified elastic solution of Hertz. The contact area under different indentation depths is also investigated. The force-displacement curve under different maximum indentation depths is obtained to investigate elastic-plastic deformation during the loading and unloading processes.Copyright

Yield Inception of a Coated Substrate Indented by a Rigid Sphere

Yield inception of a coated substrate indented by a rigid sphere is analyzed using finite element analysis. The critical interference is studied as a function of film thickness and material properties of both the film and the substrate. The results show that critical interference, corresponding to yield inception of the coated substrate, is a strong function of the film thickness, the Young’s modulus, and the yield strength of both the film and the substrate.© 2011 ASME

Mechanical properties and fracture behavior of SiCw reinforced Al–12Ti alloy prepared by bechanical alloying technique

Abstract Room and elevated temperature mechanical properties and thermal stability of SiC whisker (SiCw) reinforced Al–12Ti alloys fabricated by mechanical alloying were investigated. The results show that SiCw/Al–12Ti composites manifest higher room and elevated temperature strength and Youngs modulus and specific strength and stiffness with increasing SiCw content, which can be attributed to the combined strengthening from Al 3 Ti particles and SiC whiskers. The combined strengthening effect is especially good for lower SiCw content. The thermal stability of the composites at 550°C worsens compared to that of the unreinforced MA Al–12Ti alloy. The in situ crack propagation observation under SEM shows that the fracture behavior of SiCw/Al–12Ti composites substantially differs from that of the MA Al–12Ti alloy, but changes slightly with increasing SiCw content. The strengthening mechanisms of the composites are also discussed.