Effect of Al and Cu Contents on Mechanical Properties of Au-Cu-Al Shape Memory Alloys

Abstract

In order to develop high performance biomedical shape memory alloy having both good biocompatibility and high X ray radiography resolution, effects of Al and Cu contents on the martensitic transformation, microstructure and mechanical properties of AuCuAl ternary alloys were studied. Differential scanning calorimetry revealed that the martensitic transformation start temperature decreased with a rate of -7 K/molAl in the Au 30 molCu Al alloys. Besides, the M s increased with a rate of 18 ～53 K/molCu in the Au Cu 15～20 molAl alloys in the Cu poor side of stoichiometry, while the M s was almost constant in Cu rich side. By taking into account of the estimated defect structures, the number of Au Al atomic bonds is important for the stabilization of the parent b phase. Corresponding microstructural change due to the martensitic transformation was confirmed by optical microscopy. Vickers hardness of the Au 30 molCu Al alloys decreased with increasing Al content, and a minimum was reached at 20～25 molAl and then the Vickers hardness increased at 25 molAl. The alloys at a limited composition range around Au 30～31 molCu 14～15 molAl possessed both high strength and ductility in addition to pseudoelasticity, while the other alloys exhibited poor ductility.

Compressive Deformation Behavior and Magnetic Susceptibility of Au₂CuAl Biomedical Shape Memory Alloys

“…Microstructure of 25Cu was reported. 13) Figure 3 shows stress-strain curves by the compression tests at 298 K. All of the alloys, except 40Cu, did not break during the compression but showed plastic deformation. Especially, 25Cu, 30Cu and 45Cu had good compressive deformability over 5%, and these results were quite different from those obtained by tensile tests.…”

“…Especially, 25Cu, 30Cu and 45Cu had good compressive deformability over 5%, and these results were quite different from those obtained by tensile tests. 13) Therefore, it was revealed that (1) intergranular fracture is well suppressed during compression, and (2) Au 2 CuAl is not intrinsically brittle when grain boundary fracture is suppressed. Moreover, 25Cu, 30Cu and 45Cu all exhibited a two-stage yielding behavior.…”

“…12) Then, we have investigated the tensile mechanical properties of ternary AuCuAl alloys, and found that they are brittle when the Al content is higher than 15 mol%. 13) In addition, the fracture mode is intergranular fracture, and Fe addition enhances ductility. 14) However, there is still no classification on plastic deformation behavior of ternary Au 2 CuAl.…”

Theoretical and Experimental Designs on Several Mechanical Properties of Cu–Al–Zn Shape Memory Alloys Used in the Processing Industry

“…Shape memory alloys can be classified into the following groups according to the nature of the chemical elements found in their composition: Alloys based on Ni–Ti [ 2 , 7 , 8 , 9 ]; Copper-based alloys (Cu–Al–Zn, Cu–Al–Ni) [ 10 , 11 , 12 , 13 ]; Ferrous alloys (Fe–Mn, Fe–Ni–C) [ 14 , 15 , 16 , 17 , 18 , 19 ]; Noble alloys (Au–Cd, Ag–Cd) [ 20 , 21 , 22 ]; ”Exotic” alloys (In–Te, In–Cd, V–Nb, etc) [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. …”