Abstract:Abstract. TiNi shape-memory properties are successfully used today for the fabrication of various technical devices. The limited machinability and high cost of TiNi encourage the use of near-net shape production techniques such as metal injection moulding. In this work TiNi alloys tensile test specimens are produced by metal injection moulding from pre-alloyed powders. A binder based on a mixture of polyethylene, paraffin wax and stearic acid is used. Parts with a density of about 96.6% of theoretical density … Show more
“…The micrographies of 3D objects from composition C (NiTi + 5 wt.% TiH 2 ) show a significant difference from the other compositions. The white phase, identified as Ni 3 Ti, is not present in composition C. Similar to the other compositions, the Ni:Ti ratio also suggests the formation of phases constituted by Ni and Ti, although enriched in Ni, such as Ni 3 Ti 2 and/or Ni 4 Ti 3 [ 29 , 30 , 31 , 32 ] ( Figure 8 , Table 8 ). Moreover, a slight increase of the NiTi 2 content is also evident.…”
Shape Memory Alloys (SMAs) can play an essential role in developing novel active sensors for self-healing, including aeronautical systems. However, the NiTi SMAs available in the market are almost limited to wires, small sheets, and coatings. This restriction is mainly due to the difficulty in processing NiTi through conventional processes. Thus, the objective of this study is to evaluate the potential of one of the most promising routes for NiTi additive manufacturing—material extrusion (MEX). Optimizing the different steps during processing is mandatory to avoid brittle secondary phases formation, such as Ni3Ti. The prime NiTi powder is prealloyed, but it also contains NiTi2 and Ni as secondary phases. The present study highlights the role of Ni and NiTi2, with the later having a melting temperature (Tm = 984 °C) lower than the NiTi sintering temperature, thus allowing a welcome liquid phase sintering (LPS). Nevertheless, the reaction of the liquid phase with the Ni phase could contribute to the formation of brittle intermetallic compounds, particularly around NiTi and NiTi2 phases, affecting the final structural properties of the 3D object. The addition of TiH2 to the virgin prealloyed NiTi powder was also studied and revealed the non-formation of Ni3Ti for a specific composition. The balancing addition of extra Ni revealed priority in the Ni3Ti appearance, emphasizing the role of Ni. Feedstocks extruded (filaments) and green strands (layers), before and after debinding & sintering, were used as homothetic of 3D objects for evaluation of defects (microtomography), microstructures, and mechanical properties. The composition of prealloyed powder with 5 wt.% TiH2 addition after sintering showed a homogeneous matrix with the NiTi2 second phase uniformly dispersed.
“…The micrographies of 3D objects from composition C (NiTi + 5 wt.% TiH 2 ) show a significant difference from the other compositions. The white phase, identified as Ni 3 Ti, is not present in composition C. Similar to the other compositions, the Ni:Ti ratio also suggests the formation of phases constituted by Ni and Ti, although enriched in Ni, such as Ni 3 Ti 2 and/or Ni 4 Ti 3 [ 29 , 30 , 31 , 32 ] ( Figure 8 , Table 8 ). Moreover, a slight increase of the NiTi 2 content is also evident.…”
Shape Memory Alloys (SMAs) can play an essential role in developing novel active sensors for self-healing, including aeronautical systems. However, the NiTi SMAs available in the market are almost limited to wires, small sheets, and coatings. This restriction is mainly due to the difficulty in processing NiTi through conventional processes. Thus, the objective of this study is to evaluate the potential of one of the most promising routes for NiTi additive manufacturing—material extrusion (MEX). Optimizing the different steps during processing is mandatory to avoid brittle secondary phases formation, such as Ni3Ti. The prime NiTi powder is prealloyed, but it also contains NiTi2 and Ni as secondary phases. The present study highlights the role of Ni and NiTi2, with the later having a melting temperature (Tm = 984 °C) lower than the NiTi sintering temperature, thus allowing a welcome liquid phase sintering (LPS). Nevertheless, the reaction of the liquid phase with the Ni phase could contribute to the formation of brittle intermetallic compounds, particularly around NiTi and NiTi2 phases, affecting the final structural properties of the 3D object. The addition of TiH2 to the virgin prealloyed NiTi powder was also studied and revealed the non-formation of Ni3Ti for a specific composition. The balancing addition of extra Ni revealed priority in the Ni3Ti appearance, emphasizing the role of Ni. Feedstocks extruded (filaments) and green strands (layers), before and after debinding & sintering, were used as homothetic of 3D objects for evaluation of defects (microtomography), microstructures, and mechanical properties. The composition of prealloyed powder with 5 wt.% TiH2 addition after sintering showed a homogeneous matrix with the NiTi2 second phase uniformly dispersed.
“…The impurity levels and carbide fractions of investigated β TNZ and TNZY alloys produced by using different processing parameters are listed in Table 2. Figure 2 Carbon and oxygen contents of MIM β titanium alloys from literature [10, 15–18, 24–40]. …”
Section: Resultsmentioning
confidence: 99%
“…Oxygen and carbon are the most concerned interstitial impurities that can significantly influence the mechanical properties of MIM titanium alloys [8]. Corresponding impurity pick-up levels of β titanium alloys fabricated by up-to-date binder-based powder technologies [10,[15][16][17][18][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] are plotted in Figure 2. Apparently, oxygen levels always are in the range of 1500−3800 μg/g, while carbon levels are around 400 −800 μg/g in most cases.…”
The β titanium alloys are key materials in lightweight and biomedical applications, due to the combination of excellent biocompatibility and mechanical properties. However, the Binderbased Powder Technologies such as Metal-Injection-Molding (MIM), Binder-Jetting and Fused-Filament-Fabrication, normally introduce three major processing-related defects in the as-sintered Ti-parts: (i) residual porosity, (ii) high impurity level and (iii) coarse-grained structure. The previous studies revealed that these processing defects invariably tend to be even more severe in β titanium alloys than in α/β Ti-6Al-4V alloy, all fabricated by powder metallurgical route. In this work, these processing defects and their likely origins in MIM β titanium alloys are analysed. Furthermore, the influence of these defects on damage tolerance and fracture mechanisms of MIM β titanium alloys under either static or dynamic loading is investigated. Based on the studies, strategic technical improvements in the processing to improve the reliability of MIM β titanium alloys products are proposed.
“…During sintering, there is a chance of swelling of the compounds and this can be reduced by using pre-alloyed materials. MIM has the advantage of having fewer impurities and denser homogeneity (Bidaux et al, 2016; Guoxin et al, 2008; Schöller et al, 2005). In SPS, the surfaces of the powdered particles are melted or vaporized by spark plasma of very high localized temperature, produced by high-energy low-voltage pulsed current.…”
The current generation of automobiles is known for its sophisticated safety, comfort, and performance characteristics, which were developed in order to meet the ever-growing competition and advancement in the automotive field. Consequently, the development of smart materials with unique and exceptional properties is also gaining momentum. Of the various smart material currently applied in automotive technology, Shape Memory Alloys (SMAs), which boast the unique properties of shape memory effect and pseudo-elasticity, are steadily gaining popularity. The most prevalent automotive application of this material is in SMA actuators. These actuators are compact, lightweight alternatives to mechanical actuators, providing silent operation, enhanced reliability, durability, and resistance to humidity, shock, and vibrations. They are used in a variety of automotive systems such as adjustable mirrors, windshield wipers, door locks, smart bonnets, tumble flaps, governor valves, fog louvers, hatch vents, and many more. Among the various commercially available SMAs, Ni-Ti alloys are the most extensively used in most of these applications. This paper provides an overview of the properties, applications, and challenges of SMAs in the automotive sector.
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