Q.X. Dai

Crystal morphology and growth mechanism of reinforcements synthesized by direct melt reaction in the system Al–Zr–O

Abstract In-situ Al 3 Zr and Al 2 O 3 particulates reinforced aluminum matrix composites were fabricated by the direct melt reaction (DMR) technique in the system Al–Zr–O. Microstructures of the composites and crystal morphology of in-situ formed Al 3 Zr and Al 2 O 3 particulates were analyzed by scanning-electron microscope (SEM) and transmission electron microscope (TEM). Results indicated that in-situ formed Al 3 Zr and Al 2 O 3 particles were finer and well distributed in aluminum matrix. Al 3 Zr particulates with a tetragonal structure are mainly in the shape of polyhedron. A few of them are rectangular. The length/width ratio of the rectangular Al 3 Zr is less than 2.0 and the maximum size is 4 μm. In addition, submicro Al 2 O 3 particles with a hexagonal structure were also found in this system. Furthermore, it is found that twin may appear in the Al 3 Zr crystal. The twin plane is (1 14 ). The twinning direction is [221].

Structural parameters of the martensite transformation for austenitic steels

The effects of stacking-fault energy and strength on phase transformations in cryogenic austenitic steels are considered. An expression, which relates the transformation critical resolved shear stress, the stacking-fault energy and the strength of austenite, which is deduced to be τCi=Ai·(γSF/b)+Bi·σ0.2γ. In addition, the structural parameter, S, for the phase transformation of austenite, γSF/(σ0.2γ·b), has a great effect on the characteristics of the phase transformation. By testing and verifying, when S>0.65, γ→α, and when S<0.4, γ→e, and when S=0.35–0.65 and γ→α+e, respectively. Only if (C+N)<0.1%, does γSF become a chief factor affecting the phase transformation.