Tensile Properties of Bi Alloys and a Case Study for Alloy Design in Their Application to High Temperature Solders

Abstract

The s-orbital energy levels (Mk) of some alloying elements in a Bi cluster model were obtained on the basis of the molecular orbital calculation. In contrast, binary Bi-Cu/-Ag/-Zn system alloys with ΔMk of 0.013-0.343 were manufactured and tension-or hardness-tested, where ΔMk was the compositional average of Mk. The ultimate tensile strength and hardness were improved as alloying elements were added and increased in alloys. There was the relation between the ultimate tensile strength, fracture strain or hardness and ΔMk. Further, the compositions of Bi-2.0Ag-0.5Cu (ΔMk: 0.180), Bi-5.0Ag-0.5Cu (ΔMk: 0.379) and Bi-0.25Cu-0.25Sb (ΔMk: 0.044) were proposed as ternary alloys. It is found that the ultimate tensile strength, fracture strain and hardness values of ternary alloys could be also able to predict using their estimation lines obtained from binary Bi system alloys.

High Temperature Characterization of Binary and Ternary Bi Alloys Microalloyed with Cu and Ag

“…The 0.2% proof stress and ultimate tensile strength increased with an increase in Mk till approximately 0.18 and then remained almost constant; this was regardless of the type and amount of binary and ternary alloying elements used. This relationship at 423 K was similar to that seen at 293 K 22) . The 0.2% proof stress and ultimate tensile strength of pure Bi for a Mk of 0.00 could be also tted using the relationship between the parameters and the Mk value for the experimental alloys.…”

“…Figure 4 shows the nominal stress-strain curves for 7 of the binary Bi system alloys as determined through tensile tests at 423 K; that for pure Bi is shown as a reference. Typical softening can be seen in the stress-strain curves as compared to the curves obtained at 293 K 22) . The ultimate tensile strength and fracture strain of pure Bi were 4.2 MPa and 15.4%, respectively.…”

“…An s-orbital energy level exists above the Fermi energy level of an MBi 7 cluster 22) consisting of an alloying element M that is surrounded by Bi atoms. Therefore, the alloying effects were inevitably involved in this Mk parameter.…”

“…Fig. 4 Stress-strain curves at 423 K for Bi-0.15Cu 22) , Bi-0.25Cu, Bi-0.5Cu 22) , Bi-0.75Cu 22) , Bi-1.0Cu, Bi-2.5Ag, and Bi-5.0Ag alloys and pure Bi 22) . *Range of reduction in area (%) after failure.…”

“…We were able to determine the Mk value of a few alloying elements in a Bi cluster model by using the DV-Xα cluster method 22) . It was observed that there exists a relationship between the ultimate tensile strength or fracture strain at 293 K and Mk in the case of binary Bi-Cu/-Ag/-Zn alloys with near-eutectic compositions and that this relationship was in keeping with the results of tensile tests performed at 293 K for ternary Bi-Ag-Cu alloys 22) . These ternary alloys exhibited the desired properties, namely, a ultimate tensile strength of 20 MPa and fracture strain of 5% at 293 K 23) .…”