Microstructure and Tensile Properties of As-Cast Mg-5Sn-4Cu Alloy

The microstructure and tensile properties of permanent-mould cast Mg-5wt%Sn-4wt%Cu alloy was investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and tensile test in this paper. The result indicated that the microstructures of the as-cast samples consist of 30-40 μm size primary solidification phase, primary dendrite Mg2(Cu,Sn) which is a network-like interdendritic eutectic intermetallic compounds along grain boundaries and particle like Mg2(Sn,Cu) phases. The Mg-5Sn-4Cu alloy exhibit maximum ultimate tensile strength and yield strength, and the values are 142 MPa and 91 MPa at room temperature. This improved mechanical property is mainly ascribed to the formation of network-like secondary phases of primary dendrite Mg2(Cu,Sn).

Liquidus projection of the ternary Ag–Sn–Ni system

The liquidus projection of the ternary Sn–Ag–Ni system at the Sn-rich side was determined experimentally. No ternary compound was found, and the ζ–Ag4Sn, Ag3Sn, and Sn existed as the primary solidification phases only in very small compositional portions of the ternary Sn–Ag–Ni system. In more than half of the compositional regime of the ternary system, the Ni3Sn2 phase was the primary solidification phase. The differential thermal analysis technique was used to determine the reaction temperatures and solidification sequences of various Sn-rich Sn–Ag–Ni alloys. Three invariant reactions were found: L = Sn + Ni3Sn4 + Ag3Sn, L + ζ–Ag4Sn = Ni3Sn4 + Ag3Sn and L + Ni3Sn2 = ζ–Ag4Sn + Ni3Sn4. Their reaction temperatures have been determined to be 219, 488, and 516.5 °C, respectively.

Phase Stability, Microstructure and Mechanical Properties in the Multi-Phse Alloys Based on the L12-Ni3(Al,Be)

Intermetallic alloys based on the Ll2 Ni3(Al,Be) phase in the ternary Ni-Al-Bc system are prepared so that the alloys are multi-phase with the B2 intermetallic compound NiBe and a Ni primary solid solution denoted as (Ni). Such three-phase alloys, Ni-16 to 20 at%Al-10 at%Be, exhibit good room temperature ductility as measured by four-point bending. In order to examine the phase stabilities and relations among constituent phases, a vertical section of the ternary system is constructed at a constant 10 at%Bc mainly by differential thermal analysis. It is found that improvement in room temperature ductility can be achieved by the formation of a fine mixture of constituent phases during invariant reactions during solidification, which is further enhanced by the co-existence of the Ll2 phase formed as the primary solidification phase.

Influence of growth parameters on the microstructure of directionally solidified Bi2Sr2CaCu2Oy

Laser-heated float zone growth was used to study the directional solidification behavior of Bi–Sr–Ca–Cu–O superconductors. The phases that solidify from the melt, their morphology, and their composition are altered by growth rate. Highly textured microstructures are achieved by directional solidification at all growth rates. The superconducting phase is found always to have the composition Bi2.5Sr2CaCu2.2Oy when grown from boules with composition 2:2:1:2 (BiO1.5:SrO:CaO:CuO). Planar growth fronts of Bi2.5Sr2CaCu2.2Oy are observed when the temperature gradient divided by the growth rate (G/R) is larger than 3 ⊠ 1011 K-s/m2 in 2.75 atm oxygen. Thus, the 2212 compound was observed to solidify directly from the melt at the slowest growth rates used in this study. Measurement of the steady-state liquid zone composition indicates that it becomes bismuth-rich as the growth rate decreases. Dendrites of the primary solidification phase, (Sr1−xCax)14Cu24Oy, form in a matrix of Bi2.5Sr2CaCu2.2Oy when G/R is somewhat less than 3 ⊠ 1011 K-s/m2. Observed microstructures are consistent with a peritectic relationship among Bi2.5Sr2CaCu2.2Oy, (Sr1−xCax)14Cu24Oy (x = 0.4), and a liquid rich in bismuth at elevated oxygen pressure. At lower values of G/R, Sr3Ca2Cu5Oy is the primary solidification phase and negligible Bi2.5Sr2CaCu2.2Oy forms in the matrix.