Structural characteristics of NiTi alloys after thermal treatment

Abstract

The study of the effect of thermal treatment conditions on NiTi alloy used in biomedicine was carried out. The experimental samples of NiTi alloy with 55.8 wt% Ni were subjected to the heat treatment. The thermal regimes consisted of aging treatment at 300, 350 and 400 °C for 30 minutes followed by air cooling. The microstructures before and after the heat treatment were observed by optical microscopy. The study was completed by the microhardness measurement and XRD analysis. The obtained results show that the aging temperatures led to microstructural and microhardness changes for the investigated alloy.

Functional and Mechanical Properties of As-Deposited and Heat Treated WAAM-Built NiTi Shape-Memory Alloy

“…The average grain size was estimated by the intersection method: three random straight lines were drawn through the horizontal and vertical directions of the micrographs; the number of grain boundaries crossing the lines was counted; the length of the lines was divided by the number of intersections, and the obtained values were taken as the specific (width or height) average grain sizes. In order to investigate the influence of heat treatment on the microstructure, phase composition, mechanical properties, and functional properties of the as-deposited metal, aging treatment was utilized at a temperature of 430 • C for 1 h; it corresponds to the aging processes in the Ni-rich TiNi alloys [31].…”

“…The abovementioned microstructure characterization also fits with the one ob with higher magnification obtained with SEM in Figure 3a-c. Observations with optical microscopy of the heat-treated specimen (see Fi show a fine martensitic microstructure with a high angle of disorientation [31]. The SEM microstructure analysis of the heat-treated metal (Figure 5) shows the fo mation of new phases; for example, near-globular-shape dark points in the microstructur are either the traces of precipitates grinded during the metallographic preparation proces or are precipitates themselves.…”

“…Observations with optical microscopy of the heat-treated specimen (see Figure 4) show a fine martensitic microstructure with a high angle of disorientation [31].…”

A Review on Additive Manufacturing Methods for NiTi Shape Memory Alloy Production

“…The chemical composition of the NiTi alloy, processing parameters, and thermal or thermomechanical treatment significantly influence the microstructural changes and final properties of the products [ 100 , 101 , 102 ]. These properties can be assessed through various physical, chemical, and mechanical methods, including microscopy techniques, thermal analysis, X-ray analysis, resistivity measurement, and mechanical testing [ 103 , 104 , 105 ].…”

“…Etching the polished surface usually reveals martensite–austenite phases or grain size. Common etching solutions include HF:HNO 3 :CH 3 COOH (3:5:3 ratio) for phases or HF:HNO 3 :H 2 O (2:5:10 ratio) for grain size [ 103 , 104 , 105 ]. SEM analysis provides detailed observations of topographic features, small particles, fracture surfaces, pores, and Ni 4 Ti 3 precipitates, offering deeper insights compared to optical microscopy.…”