REGULARITIES OF MACROPLASTIC DEFORMATION OF NARROW-BAND SINGLE CRYSTALS OF CdxHg 1-xTe SOLID SOLUTIONS

The regularities of macroplastic deformation of narrow-band semiconductors of HgTe-CdTe solid solution crystals were studied by the uniaxial compression method on a Regel-Dubov relaxometer. The four-stage character of the strain hardening curve “stress-strain” is established. The influence of stoichiometry, load velocity and temperature on the nature of load curves is investigated. From the experiments on the relaxation of mechanical stresses, a thermoactivation analysis of the kinetics of microplastic deformation was performed. Thermoactivation parameters of dislocation motion are estimated. The criteria for performing the Pierrels mechanism of dislocation motion in these crystals are investigated. The influence of light on the macroplastic fluidity of CdxHg1-xTe crystals is described.

INVESTIGATION OF THE STRUCTURE AND PROPERTIES OF WEAR-RESISTANT SURFACED ALLOY SYSTEM FE - C - CR - NI - MN - MO - TI - NB

Metallographic studies of the microstructure of the experimental type of the deposited alloy of the Fe - C - Cr - Ni - Mn - Mo - Ti - Nb alloying system were performed. The chemical and granulometric composition of the metal-strengthening phases has been determined. The weld metal was tested for resistance to gas-abrasive wear at elevated temperatures. The wear resistance of the deposited metal was diagnosed by sclerometry with obtaining images of tracks from the indenter using atomic force microscopy. The character of microplastic deformation of worn surface layers of the alloy is investigated. The influence of the structural phase composition and hardening phases in the deposited metal on its wear resistance is discussed. Promising ways to further increase the resistance of the experimental alloy to gas-abrasive wear are determined.

High Cycle Fatigue Damage Evaluation of Steel Pipelines Based on Microhardness Changes During Cyclic Loads: Part II

The hardness of a material shows its ability to resist to microplastic deformation caused by indentation or penetration and is closely related to the plastic slip capacity of the material. Therefore, it could be significant to study the resistance to microplastic deformations based on microhardness changes on the surface, and the associated accumulation of fatigue damage. The present work is part of a research study being carried out with the aim of proposing a new method based on microstructural changes, represented by a fatigue damage indicator, to predict fatigue life of steel structures submitted to cyclic loads, before macroscopic cracking. Here, Berkovich indentation tests were carried out in the samples previously submitted to high cycle fatigue (HCF) tests. It was observed that the major changes in the microhardness values occurred at the surface of the material below 3 μm of indentation depth, and around 20% of the fatigue life of the material, proving that microcracking is a surface phenomenon. So, the results obtained for the surface of the specimen and at the beginning of the fatigue life of the material will be considered in the proposal of a new method to estimate the fatigue life of metal structures.

Gear Wheels Surface Engineering by Deformation Hardening and Carburization

The purpose of research is to determine the influence of carburized layer initial structural condition on the plastic deformation hardening. Deformation hardening in combination with low temperature tempering is an important technological factor of martensite or martensite-austenite matrix management of carburized layer. The formation of favorable substructure - substructure with high resistance to local microplastic deformation - occurs in the conditions of competitive processes development. The initial structural condition of carburized layer renders the influence on those processes development degree. The initial structural conditions are determined by the termochemical treatment technology. The latter relates to: the carbon saturation of carburized layer; martensite morphology and carbon concentration in it; volume fraction of redundant carbide phase and its distribution through the carburized layer; the presence of retained austenite.