“…Furthermore, the irregular and nonuniform shape and distribution are mainly acted to increase the internal stress and allow the crack to be propagated easily, and thus reduce the mechanical and shape memory properties. 23,31–33 Figure 2.Optical micrographs of Ti–30% Ta samples were sintered at (a) and (b) 900℃, (c) and (d) 1000℃, and (e) and (f) 1200℃, while the sintering time of (a, c, and e) for 10 min and (b, d, and f) for 30 min.…”
Section: Resultsmentioning
confidence: 99%
“…MWS integrates pre-alloyed elements and absorbs electromagnetic energy using volumetric means and leading to transformation into heat. 21–23 MWS is different from other sintering technologies and provides the following benefits: it has a rapid rate of heating, uses less amount of energy, reduces the time used for sintering, enhances mechanical and physical properties of the materials being sintered, and results in the improvement of element diffusion process. 21 In several types of research, the MWS technique used produces Ti and its alloys such as Ti–Ta–Sn, Ti–Nb, and Ti–Nb–Sn.…”
In this work, the influence of microwave sintering time and temperature on the microstructure characterisation, and thermal and mechanical behaviours of Ti–30Ta were investigated. The relative densities of Ti–30Ta samples were in the range of 65–72% and as the sintering times/temperatures increased, the relative density decreased. The pore size averages were in the range of 6–17 µm with different sintering parameters, for instance the smallest pore size of 6.8 µm was observed after being sintered at 900 ℃ for 30 min (Ta2). Two morphologies of plate-like (P) and needle-like (N) structures were observed, as well as two regions – dark region (Ti-rich region) and bright region (Ta-rich region), also two phases – β and α. The DSC results revealed that the Ms to Mf transformation range was 98.86 to 80.5 ℃, respectively, while the range of As to Af transformation was about −22.35 to 92 ℃, respectively. The maximum fracture strength and its strain were acquired in the sintered sample of 900 ℃ for 30 min. The total strain recovery (ɛT) was improved linearly as the sintering temperature increased, correspondingly, the best ɛT was implied in Ti–Ta shape memory alloys after being sintered at 1000 ℃ for 30 min (Ta4).
“…Furthermore, the irregular and nonuniform shape and distribution are mainly acted to increase the internal stress and allow the crack to be propagated easily, and thus reduce the mechanical and shape memory properties. 23,31–33 Figure 2.Optical micrographs of Ti–30% Ta samples were sintered at (a) and (b) 900℃, (c) and (d) 1000℃, and (e) and (f) 1200℃, while the sintering time of (a, c, and e) for 10 min and (b, d, and f) for 30 min.…”
Section: Resultsmentioning
confidence: 99%
“…MWS integrates pre-alloyed elements and absorbs electromagnetic energy using volumetric means and leading to transformation into heat. 21–23 MWS is different from other sintering technologies and provides the following benefits: it has a rapid rate of heating, uses less amount of energy, reduces the time used for sintering, enhances mechanical and physical properties of the materials being sintered, and results in the improvement of element diffusion process. 21 In several types of research, the MWS technique used produces Ti and its alloys such as Ti–Ta–Sn, Ti–Nb, and Ti–Nb–Sn.…”
In this work, the influence of microwave sintering time and temperature on the microstructure characterisation, and thermal and mechanical behaviours of Ti–30Ta were investigated. The relative densities of Ti–30Ta samples were in the range of 65–72% and as the sintering times/temperatures increased, the relative density decreased. The pore size averages were in the range of 6–17 µm with different sintering parameters, for instance the smallest pore size of 6.8 µm was observed after being sintered at 900 ℃ for 30 min (Ta2). Two morphologies of plate-like (P) and needle-like (N) structures were observed, as well as two regions – dark region (Ti-rich region) and bright region (Ta-rich region), also two phases – β and α. The DSC results revealed that the Ms to Mf transformation range was 98.86 to 80.5 ℃, respectively, while the range of As to Af transformation was about −22.35 to 92 ℃, respectively. The maximum fracture strength and its strain were acquired in the sintered sample of 900 ℃ for 30 min. The total strain recovery (ɛT) was improved linearly as the sintering temperature increased, correspondingly, the best ɛT was implied in Ti–Ta shape memory alloys after being sintered at 1000 ℃ for 30 min (Ta4).
“…The authors, however, speculated that this was "related to a change in aspect ratio of the wall thickness against the edge length" [35]. Unlike the aforementioned research works wherein increasing pore size resulted in either increasing or decreasing the compression strength, in the study of Xu et al on biomedical porous NiTi alloys, [36] the strength values varied with pore sizes in a "S type" fashion, i.e., as the pore size increased once, the value of the strength dropped initially, and after the second and third increase of the pore size, the strength increased and decreased, respectively. They attributed this behavior of porous NiTi alloys to the pore size as well as the number of pores both of which represent the same effect on the mechanical properties of the porous alloys, i.e., the increase of the pore size and the number of pores would result in a decrease in the value of mechanical properties including the Rockwell hardness, compression strength and elastic modulus.…”
Section: Effect Of Structural Properties On Elastic and Plastic Comprmentioning
Biodegradable metal foams have been studied as potential materials for bone scaffolds. Their mechanical properties largely depend on the relative density and micro-structural geometry. In this work, mechanical behavior of iron foams with different cell sizes was investigated under various compression tests in dry and wet conditions and after subjected to degradation in Hanks' solution. Statistical analysis was performed using hypothesis and non-parametric tests. The deformation behavior of the foams under compression was also evaluated. Results show that the mechanical properties of the foams under dry compression tests had a "V-type" variation, which is explained as a function of different geometrical properties by using a simple tabular method. The wet environment did not change the compression behavior of the iron foams significantly while degradation decreased the elastic modulus, yield and compression strengths and the energy absorbability of the specimens. The deformation of open cell iron foams under compression is viewed as a complex phenomenon which could be the product of multiple mechanism such as bending, buckling and torsion.
“…Corrosion resistance of porous NiTi decreases three times as compared to dense NiTi. 86,87 The compressive strength of porous NiTi alloy was also found to be decreased from 880 to 62 MPa with increase of porosity from 22% to 62 %. The bending strength of alloy also decreased from 371.4 MPa to 74 MPa with increase of porosity.…”
Nitinol (NiTi) is categorized as a smart material which is highly recognized material for medical and other engineering applications. The behaviour of NiTi can be modified by altering the composition, modifying the porosity and applying external thermal and mechanical treatment. Due to high composition sensitivity, there are several impediments in fabrication of NiTi with conventional techniques which impel the use of additive manufacturing methods. But due to very high cost of equipments, these processes have not been commercialized till now. This paper presents a review on applications, manufacturing NiTi alloy and its various production routes from conventional to rapid prototyping, porous NiTi, effect of additives on properties of the alloy and its challenges.
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