Možnosti přípravy slitin Ni-Ti a Ni-Ti-(X) metodami práškové metalurgie

Abstract

The main characteristics alloys from Ni-Ti-(X) system, influence of alloying elements on their structure and properties, and their industrial applications are summarized in the theoretical part. The methods of their preparation using powder metallurgy techniques and the purpose of heat treatment are also described. Experimental part of the thesis was focused on the preparation of powder alloys based on NiTi and NiTiCu by mechanical alloying of pure Ni, Ti and Cu powders and on the influence of alloying conditions on the shape, morphology, size and composition of particles using SEM/EDX, laser diffraction and BET analysis. Powder alloys were then cold isostatically pressed using different pressures with the aim to determine the effect of used pressure on the achieved sintered density of samples and final porosity. Green compacts were sintered under the protective atmosphere of argon with purity 6N and also in vacuum at 1050 °C for 3 hours. Due to the presence of undesirable phases in the structure, sintered samples were subsequently heat treated at 900 °C for 24 hours followed by a quenching in cold water. Sintered and heat treated samples of NiTi and NiTiCu alloys were submitted to the structural and phase analysis by means of LOM and SEM/EDX and the total and area porosity were determined. It was found that Ni-Ti alloys have a lower porosity than Ni-Ti-Cu alloys. Samples sintered in vacuum exhibited higher porosity than the samples sintered in argon. Heat treatment influenced the final porosity of alloys. During the sintering was created several phases: NiTi (Cu) TiNi3 (Cu), Ti2Ni (Cu) and Ni2Ti (Cu). There is also occurring particles of titanium. Phase TiNi3(Cu) was partially dissolved, during the heat treatment.