Effect of Destined High-Pressure Torsion on the Structure and Mechanical Properties of Rare Earth-Based Metallic Glasses
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INTRODUCTION
BULK metallic glasses (BMGs) possess isotropic properties, high strength, low friction coefficient, high wear resistance, and high corrosion resistance, all of which enable the application of BMGs in several fields.[1,2] Rare earth elements have been used as critical minor alloying additives and as the main components in BMG preparation.[3,4] Owing to the distinct electronic structure of lanthanide elements, rare earth-based BMGs (REBMGs) are considered promising materials for various practical applications and for understanding key issues in metallic glass research.[5,6] Numerous REBMGs with controlled properties have been developed,[7–9] but these REBMGs usually have low strength. Processing methods, such as low-temperature annealing,[10,11] ultrasonic treatment,[12] and hydrostatic pressure treatment,[13] have been proposed to improve the performance of BMGs. High-pressure torsion (HPT)[14] is also a relatively economical method that may have a crucial role in the future development of BMGs. The large deformation and low plasticity of BMGs, however, may eventually cause the samples to burst. This paper
W. ZHAO and M.L. WU are with the School of Materials Science and Engineering, Nanjing Institute of Technology, Nanjing 211167, China and also with the Jiangsu Key Laboratory of Advanced Structural Materials and Application, Technology, Nanjing 211167, China. Contact e-mail: [email protected] H. CHENG and G. LI are with the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China. X. JIANG is with the Insitute of Science, PLA University of Science and Technology, Nanjing 211101, China. Manuscript submitted August 20, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
proposes an improved method (i.e., destined HPT). This study explored a strengthening mechanism by focusing on the changes in the structure and mechanical properties of Pr60Cu20Al10Ni10 and Ce70Cu20Al10 metallic glasses. Analyses were performed by means of X-ray diffraction (XRD) synchrotron radiation and nanoindentation.
II.
EXPERIMENTS
Arc melting was performed to prepare rare earthbased alloys Pr60Cu20Al10Ni10 and Ce70Cu20Al10 (by atomic percentage). Copper mold casting was conducted in an argon atmosphere to produce BMG cylindrical ingots. The samples were approximately 30 mm long and 1.2 mm in diameter. Cylindrical specimens were ground on a center-less grinding machine to a diameter of 1 mm and wrapped in a mild steel sleeve, which had an external diameter of 10 mm and a thickness of 2 mm, to introduce HPT, as shown in Figure 1. The specimens were torsion strained under P = 3 GPa for N = 3 turns at a rotation speed of 0.2 rpm at room temperature. For comparison, another set of samples was not deformed and will be, henceforth, denoted as the as-cast specimens. Indentations were conducted to measure nanohardness, and the friction coefficient was determined through nanoscratching to evaluate wear resistance. Nanoindentation was measured at the edge of the cross section of each cyli
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