Investigation of the machinability by milling of the laser sintered Inconel 625/NiTi-TiB2 composite

OBRABOTKAMETALLOV Vol. 23 No. 1 2021 TECHNOLOGY Ta b l e 1 Physical and mechanical properties of the Inconel 625 and NiTi-TiB 2 composite Physical and mechanical properties Value Density, g / cm 3 8.3 Compressive strength, MPa 1830 Tensile strength, MPa 860 Bend strength, MPa 1320 Compression fl ow stress, MPa 990…1090 Tensile fl ow stress, MPa 110…160 Modulus of elasticity, GPa 290…330 Poisson’s ratio 0.29 Coef fi cient of thermal conductivity, W/m K 12.5…13.6 Coef fi cient of linear thermal expansion, K –1 11.3…12.4 ∙ 10 –6 Hardness ( H V ), HRC 44….46 This paper considers a laser sintered composite based on Inconel 625 with the addition of NiTi-TiB 2 ceramic particles to its matrix [2]. This composite was obtained at High-Energy and Special Materials Research Laboratory, Tomsk State University for the manufacture of turbine blades [1]. The blades of gas turbines operate at high temperatures and loads. The alloys used for the manufacture of turbo engine parts must have high strength, toughness, heat resistance, and corrosion resistance [3]. In Russia, nickel- based alloys are used for the manufacture of turbine blades, for example, such brands as KhN35VTYu, KhN55VMTKYu, KhN62MVKYuL, KhN67MVTYuL, KhN70MVTYuB, KhN75VMYu, KhN80TBYu, ZhS6UD [4]. The properties of these alloys today do not always meet the requirements. Importantly, the products or workpieces obtained using additive technologies may have a higher tensile strength and fl ow stress as well as low elongation values compared to samples obtained by casting and rolling [5]. The disadvantage of composites obtained by additive technologies is the uneven distribution of the added particles inside the metal matrix, which signi fi cantly reduces their physical and mechanical properties. The method of obtaining a composite proposed by the authors [1] reduces this disadvantage to a minimum. For this study, samples were taken in the form of bars; their chemical composition, some physical and mechanical properties are presented in Table 1. The composite obtained in the study [1] is characterized by increased wear resistance and heat resistance. Since the material is new, its machinability by cutting has not yet been studied. This paper presents a study of this composite machinability by milling. The term machinability is seen as the property of metals to be processed by cutting. According to [6], the main indicators for assessing machinability are such parameters as cutting forces, the quality of the surface layer, tool wear, the heat released during deformation of the cut layer material, the presence or absence of a tendency to build up, as well as the type, shape, and size of the cut chips. Depending on these characteristics, all materials are divided into 8 groups [4]. According to the recommendations from the reference manual [4], the chemical composition of the Inconel 625 composite with NiTi-TiB 2 corresponds to the V-VI group of machinability. These groups include heat-resistant, refractory, acid-resistant steels as well as nickel-and iron-nickel-based alloys. These groups have very low machinability with a coef fi cient of 0.16...0.08 in comparison with steel 45, whose coef fi cient is 1. Low machinability is associated with high tensile strength and hardness, which have a signi fi cant impact on the cutting forces during processing. The cutting forces during the processing of sintered alloys may be greater than the forces arising when cutting similar alloys obtained by classical