Microstructure and physical-mechanical properties evolution of pure tantalum processed with hard cyclic viscoplastic deformation

• Published in: International journal of refractory metals & hard materials 2019-09, Vol.83, p.104983, Article 104983
• Main Authors: Kommel, Lembit, Shahreza, Babak Omranpour, Mikli, Valdek
• Format: Article
• Language: English
• Subjects: Deformation; Density; Electrical conduction; Electrical resistivity; Electron beams; Equal channel angular pressing; Fracture mechanics; Hard cyclic viscoplastic deformation; Hardness; Heat treatment; Materials testing; Mechanical properties; Microstructure; Modulus of elasticity; Physical properties; Severe plastic deformation; Strain rate; Tantalum
• ISSN: 0263-4368; 2213-3917
• DOI: 10.1016/j.ijrmhm.2019.104983

The techniques of equal channel angular pressing and hard cyclic viscoplastic deformation were used to make changes in the microstructure and physical-mechanical properties of commercially pure tantalum. For the experiments, we used double electron beam melted oligocrystalline tantalum billet that was previously heat treated at 1100 °C for 1 h and processed by equal channel angular pressing with a wide range of equivalent von Mises strain (ℇVM = 0÷13.8) imposed on materials. At follows, the samples with stepped cross sections were tested on a materials testing setup Instron-8516 at room temperature. These changes in tantalum were determined depending on the tension-compression strain amplitude, strain rate, cycling frequency and number of cycles. The effects of processing routines on changes in the microstructure were investigated using scanning electron microscope and X-ray techniques. The mechanical and physical properties changes were characterized using hardness, density and electrical conduction measure techniques. The fracture mechanics change was studied by mini samples tensile testing up to fracture. The results show that during hard cyclic viscoplastic deformation of equal channel processed samples, with different processing histories, the tensile strength, hardness, plasticity, density, electrical conductivity, Young's modulus, etc. are changed. These changes in tantalum were characterized and analyzed. [Display omitted] •Tensile strength of pure Ta was increased from 200 MPa to 800 MPa.•Young's modulus of pure Ta was changed from 141 GPa to 220 GPa.•Density of pure Ta was increased from 16.25 g·cm−3 to 16.78 g·cm−3.•Grain boundaries of pure Ta were formed on the atomic scale during HCVD.•Fracture surfaces at tension characterize the pure Ta microstructure and mechanical properties.