The impact of severe plastic deformations obtained by hydrostatic extrusion on the machinability of ultrafine-grained Ti grade 2 intended for fasteners

Abstract

The study aimed to examine the effect of the hydrostatic extrusion (HE) process on the machinability of Ti grade 2 (Ti) in the turning process. After the deformation with true strain ɛ = 2.28, the microstructure was significantly refined to a grain size of 100 nm, resulting in an increase in the mechanical properties, UTS strength by 190%, YS yield strength by 230%Cutting forces for Ti in the initial state and after HE were analyzed at cutting depths ap = 0.3 mm and 0.5 mm, the variables were cutting speed Vc (20, 30 and 50 m/min) and feed rate f (0.08 and 0.13 m/s).The impact of the microstructure refinement in Ti after HE on the high cutting depth machinability deterioration (ap = 0.7 mm) was identified. This phenomenon is particularly noticeable at lower cutting speeds Vc = 20 and 30 m/min at which cutting forces are higher. Application tests of Ti after HE showed a significantly lower susceptibility to buckling during threading. As a result of the tests carried out for the Ti in the initial state, it was not possible to achieve the tolerance of pitch diameter of the thread required by standards, d2 at two of the three cutting depths tested. In turn, for the Ti after HE, the thread tolerances required by the standards were achieved for all tested cutting depths.

The Effect of Microstructural Defects on High-Cycle Fatigue of Ti Grade 2 Manufactured by PBF-LB and Hydrostatic Extrusion

“…The selected area electron diffraction (SAED) patterns taken from the TEM images (Figure 3a) also proved to be a development of the UFG microstructure, i.e., diffraction spots formed a relatively continuous circles, which indicate high misorientation between the numerous fine grains. These microstructural characteristics of UFG Ti Grade 2 are consistent with the typical microstructures observed for Ti Grade 2 after HE to a similar accumulated true strain [32,36,37]. The microstructure of UFG Ti Grade 2 is presented in Figure 3, and it was mainly composed of fine, equiaxed α phase grains/subgrains with a size of 50-150 nm (the average grain/subgrain size was 102 ± 49 nm) and a small fraction of relatively coarse grains (with a size of several hundred nanometers) with a high density of tangled dislocations or non-fully developed dislocation cells.…”

“…The selected area electron diffraction (SAED) patterns taken from the TEM images (Figure 3a) also proved to be a development of the UFG microstructure, i.e., diffraction spots formed a relatively continuous circles, which indicate high misorientation between the numerous fine grains. These microstructural characteristics of UFG Ti Grade 2 are consistent with the typical microstructures observed for Ti Grade 2 after HE to a similar accumulated true strain [32,36,37]. The martensitic α' microstructure of PBF-LB Ti Grade 2 and the highly refined α phase microstructure of UFG Ti Grade 2 resulted in their extraordinary tensile properties, which are not commonly achieved for conventionally manufactured CP Ti [24,36].…”

“…Additionally, to To obtain UFG specimens, a commercially available Ti Grade 2 (0.17% Fe, 0.018% C, 0.009% N, 0.001% H, 0.15% O, Ti balanced) in the form of a rod with an initial diameter of 50 mm was subjected to room temperature HE in two stages: (1) from 50 to 25 mm, and (2) from 25 to 16 mm, resulting in a total accumulated true strain of ε = 2.28. The details of the HE processing can be found in [32].…”

Effect of microstructure refinement of pure copper on improving the performance of electrodes in electro discharge machining (EDM)

“…The research that has been conducted at the Institute of High Pressure Physics, Polish Academy of Sciences Unipress IHPP PAS for 45 years has confirmed the exceptional suitability of HE for generating severe plastic strains in materials, including materials that cannot be strained with the use of conventional methods such as rolling, drawing or conventional extrusion. This allows to give the materials new, higher strength 21 – 24 , fatigue 25 , impact strength 26 , tribological 27 and corrosion 28 properties, while improving functional properties such as machinability 29 , 30 or electrical conductivity 31 .…”

Thermo-Mechanical Treatment for Reducing the Wear Rate of CuCrZr Tool Electrodes during Electro-Discharge Machining

“…It has been proven repeatedly that hydrostatic extrusion promotes grain refinement with a higher efficiency than other SPD methods, also due to the higher strain rates used [20][21][22][23] and the favourable state of compressive and tensile stresses present in the deformation zone. This confers the materials with a better strength [24][25][26][27], fatigue properties [28], impact strength [29], tribological properties [30] and corrosion properties [31], while improving functional properties such as the machinability [32,33] and electrical conductivity [34].…”