An investigation into the possibility to eliminate the microstructural defects of parts printed using a Ni-rich Ni-Ti elemental powder mixture

Abstract

Ni-rich Ni-Ti alloys, such as 60NiTi, show a higher hardness and dimensional stability than equiatomic or near-equiatomic NiTinol ones. These make them suitable to be employed in structural applications. Laser powder bed fusion technique (LPBF) was used in this research to print parts from a Ni-rich Ni-Ti powder mixture consisting of about 63 wt.% Ni and 37 wt.% Ti. The microstructure of the obtained parts, processed using different parameters, showed inhomogeneity, contained undesirable Ni-rich and Ti-rich regions and a significant amount of cracks. To eliminate these defects, homogenize the microstructure and to obtain the required phases, we applied hot isostatic pressing (HIP) to the printed samples with a selected set of parameters. After HIP at 180 MPa and 1050 °C for 4 h, we observed the formation of a homogeneous microstructure containing mainly NiTi and Ni3Ti phases in the printed samples. However, cracks still persisted in the microstructure of these HIP treated samples. Applying another round of HIP treatment at a temperature just slightly above the melting start temperature of the samples, treated by the elementary HIP procedure, could successfully eliminate the cracks in the microstructure of samples and also increase the crystallinity of the existing phases.

Effect of CeO2 on crack sensitivity and tribological properties of Ni60A coatings prepared by laser cladding

“…Under the work of the high-energy laser beam, the TC4 substrate and CeO 2 /Ni-based composite powder underwent more complex physical and chemical changes in the reaction process of molten pool, which leaded to the formation of different phases. [22][23][24] The reaction equation of was shown below:…”

Effects of the process parameters on the formability and properties of Ni54(at.%) Ti alloys prepared by laser powder bed fusion

“…They found that low-power LPBF-fabricated Ni-Ti forms martensite with a better damping capacity and that different regions in the Ni-Ti have different microstructures and mechanical properties. Khanlari et al (2020) successfully fabricated an Ni-rich Ni-Ti alloy using an Ni-rich elemental powder mixture. To reduce the number of defects such as cracks, homogenize the microstructure and obtain the required phases, the authors applied hot isostatic pressing to the printed samples with a selected set of parameters.…”

“…In recent years, several researchers have successfully manufactured Ni–Ti alloys by LPBF (Khanlari et al , 2020; Habijan et al , 2013; Liu et al , 1999; Meier et al , 2009; Bormann et al , 2012; Habijan et al , 2011; Haberland et al , 2014; Dadbakhsh et al , 2014; Frenzel et al , 2010; Wang et al , 2018; Walker et al , 2016; Moghaddam et al , 2018; Chen et al , 2020; Mn et al ,2021; Tan et al , 2019). Haberland developed high quality Ni–Ti alloys by LPBF (Haberland et al , 2014).…”

“…Ni-rich Ni-Ti alloys (such as Ni54(at.%)Ti) have great potential in structural applications because of their high hardness and good shape stability. This grade of Ni-Ti alloys was used by National Aeronautics and Space Administration (NASA) for developing hard and resilient rolling bearing components (Khanlari et al, 2020). On the other hand, although Ni-Ti alloys have great application prospects, properties such as high ductility and work hardening pose very big challenges for machining such alloys (Stoeckel, 2001;Wu et al, 1999;Biermann et al, 2011; The current issue and full text archive of this journal is available on Emerald Insight at: https://www.emerald.com/insight/1355-2546.htm Bellouard, 2008).…”

Microstructure and Mechanical Properties of NiTi-Based Eutectic Shape Memory Alloy Produced via Selective Laser Melting In-Situ Alloying by Nb

“…Nitinol-based alloys, unlike Fe-and Cu-based shape memory alloys, are characterized by high strength and ductility and have high corrosion resistance and biocompatibility. However, brittle secondary phases such as the metastable compound Ni 4 Ti 3 , which can decompose into Ni 3 Ti 2 and Ni 3 Ti with increasing temperature, are commonly observed in NiTi-based alloys [5,6]. These phases increase the hardness of the material, but reduce the ductility of NiTi alloys, limiting their application.…”