Microstructure Evolution and Mechanical Properties of Titanium Nickelide during Pressing in Equal-Channel Angular Matrix with Quasi-Small Angle of Channels Intersection

The article presents the results of the analysis of the microstructure and mechanical properties of titanium nickelide formed during pressing in an equal-channel angular matrix with a quasi-small angle of channels intersection. The conducted studies have shown that pressing in an equal-channel angular matrix with a quasi-small angle of channels intersection ensures the formation of a homogeneous sub-ultrafine-grained structure in the titanium nickelide alloy, while the average grain size, decreasing by 100-200 times, is 0.3-0.5 microns, and the tensile strength increases to 1350 MPa in 6 passes, which is almost 90% higher than in the coarse-grained quenched state.

Microstructural Investigation of a Friction-Welded 316L Stainless Steel with Ultrafine-Grained Structure Obtained by Hydrostatic Extrusion

The paper presents the microstructural investigation of a friction-welded joint made of 316L stainless steel with an ultrafine-grained structure obtained by hydrostatic extrusion (HE). Such a plastically deformed material is characterized by a metastable state of energy equilibrium, increasing, among others, its sensitivity to high temperatures. This feature makes it difficult to weld ultra-fine-grained metals without losing their high mechanical properties. The use of high-speed friction welding and a friction time of <1 s reduced the scale of the weakening of the friction joint in relation to result obtained in conventional rotary friction welding. The study of changes in the microstructure of individual zones of the friction joint was carried out on an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscattered diffraction (EBSD) analysis system. The correlation between the microstructure and hardness of the friction joint is also presented. The heat released during the high-speed friction welding initiated the process of dynamic recrystallization (DRX) of single grains in the heat-affected zone (HAZ). The additional occurrence of strong plastic deformations (in HAZ) during flash formation and internal friction (in the friction weld and high-temperature HAZ) contributed to the formation of a highly deformed microstructure with numerous sub-grains. The zones with a microstructure other than the base material were characterized by lower hardness. Due to the complexity of the microstructure and its multifactorial impact on the properties of the friction-welded joint, strength should be the criterion for assessing the properties of the joint.

Effect of Hydrogen on the Deformation Behavior and Localization of Plastic Deformation of the Ultrafine-Grained Zr–1Nb Alloy

In this paper, comparison studies of the hydrogen effect on the structural and phase state, deformation behavior, and mechanical properties of the fine- (average grain size 4 µm) and ultrafine-grained (average element size 0.3 and 0.4 µm) Zr–1wt.%Nb (hereinafter Zr–1Nb) alloy under tension at temperatures in the range of 293–873 K were conducted. The formation of an ultrafine-grained structure is established to increase the strength characteristics of the Zr–1Nb alloy by a factor of 1.5–2 with a simultaneous reduction of its resistance to the localization of plastic deformation at the macro level and the value of deformation to failure. The presence of hydrogen in the Zr–1Nb alloy in the form of a solid solution and hydride precipitates increases its resistance to the localization of plastic deformation at the macro level if the alloy has an ultrafine-grained structure and decreases if the structure of the alloy is fine-grained. In the studied temperature range, the Zr–1Nb alloy in the ultrafine-grained state has a higher resistance to hydrogen embrittlement than the alloy in the fine-grained state.