Performance of Carbide Alloy Compounds in Carbon Doped MoNbTaW

In this work, the performance of the carbon doped compositionally complex alloy (CCA) MoNbTaW was studied under ambient and high pressure and high temperature conditions. TaC and NbC carbides were formed when a large concentration of carbon was introduced while synthesizing the MoNbTaW alloy. Both FCC carbides and BCC CCA phases were detected in the sample compound at room temperature, in which the BCC phase was believed to have only refractory elements MoNbTaW while FCC carbide came from TaC and NbC. Carbides in the carbon doped MoNbTaW alloy were very stable since no phase transition was obtained even under 3.1 GPa and 870 °C by employing the resistor-heating diamond anvil cell (DAC) synchrotron X-ray diffraction technique. Via in situ examination, this study confirms the stability of carbides and MoNbTaW in the carbon doped CCA even under high pressure and high temperature.

The effect of homogenization on microstructure and hardness of a large-scale high-aluminum Al4.4Co26Cr18Fe18Ni26Ti5.5 Compositionally Complex Alloy cast

As any largescale cast material, specific Compositionally Complex Alloys or High Entropy Superalloys contain segregations, leading to unideal, inhomogeneous properties. This work presents the effects of a homogenization heat treatment at 1 150°C for 6 h of a large-scale cast Al4.4Co26Cr18Fe18Ni26Ti5.5 alloy. In order to reveal these effects, homogenized specimens were analyzed and compared to the as-cast state with regard to chemical homogeneity as well as the homogeneity of elemental solution by means of scanning electron microscopy, energy dispersive X-ray spectroscopy as well as X-ray diffraction and hardness measurements. Despite the increased Al content, intermetallic phases and segregations, observable in the as-cast state, dissolve during homogenization. Improved, but not full homogeneity of elemental distribution after annealing can be determined. The improved state of solution and homogeneity agrees with the increasing lattice parameter from 3.572 Å to 3.594 Å and the decreasing hardness from 320.3 HV10 to 245.2 HV10 during homogenization.

Microstructure, Hardness, and Elastic Modulus of a Multibeam-Sputtered Nanocrystalline Co-Cr-Fe-Ni Compositional Complex Alloy Film

A nanocrystalline Co-Cr-Ni-Fe compositional complex alloy (CCA) film with a thickness of about 1 micron was produced by a multiple-beam-sputtering physical vapor deposition (PVD) technique. The main advantage of this novel method is that it does not require alloy targets, but rather uses commercially pure metal sources. Another benefit of the application of this technique is that it produces compositional gradient samples on a disk surface with a wide range of elemental concentrations, enabling combinatorial analysis of CCA films. In this study, the variation of the phase composition, the microstructure (crystallite size and defect density), and the mechanical performance (hardness and elastic modulus) as a function of the chemical composition was studied in a combinatorial Co-Cr-Ni-Fe thin film sample that was produced on a surface of a disk with a diameter of about 10 cm. The spatial variation of the crystallite size and the density of lattice defects (e.g., dislocations and twin faults) were investigated by X-ray diffraction line profile analysis performed on the patterns taken by synchrotron radiation. The hardness and the elastic modulus were measured by the nanoindentation technique. It was found that a single-phase face-centered cubic (fcc) structure was formed for a wide range of chemical compositions. The microstructure was nanocrystalline with a crystallite size of 10–27 nm and contained a high lattice defect density. The hardness and the elastic modulus values measured for very different compositions were in the ranges of 8.4–11.8 and 182–239 GPa, respectively.

Influence of modes of thermal hardening and the subsequent cryogenic processing on structure and properties of steel 38Ni3CrMoV

For the production of various machine-building products - rolling rolls, parts of power equipment, piercing mandrels - complex alloy steels containing chromium and a significant number of other deficient alloying elements (nickel, vanadium, molybdenum) type 38Ni3CrMoV are used. The paper presents the results of research on the influence of modes of hardening and subsequent cryogenic treatment on the parameters of the structure, hardness and wear resistance of this steel. Visible changes in the microstructure of thermally improved steel samples during cryogenic treatment were not found, which can be explained by the high thermodynamic stability of the sorbitol structure and the practical absence of residual austenite due to its decomposition during high tempering. It is shown that cryogenic treatment of thermally improved 38Ni3CrMoV steel contributes to an increase in the hardness, toughness and wear resistance this steel (~3.8 %). In this case, there is a slight increase in the parameter and magnitude of microstresses of the crystal lattice, an increase in the density of dislocations due to the removal of thermal stresses. To obtain a multiphase structure of 38Ni3CrMoV steel with retained austenite, isothermal quenching from the γ - α region has been proposed. The use of cryogenic treatment for the experimental mode of hardening of 38Ni3CrMoV steel samples promotes the transformation of retained austenite in the final structure of the samples into martensite with a significant increase in the microhardness of its structural components at the 22.3 %. The experimental hardening mode + cryogenic treatment provides a significant increase in the hardness and wear resistance of 38Ni3CrMoV steel at the 21.6 % while ensuring a certain level of its impact toughness (more than 4 J/cm2) and can be recommended for the implementation of the technology of differentiated hardening of large-sized products made of 38Ni3CrMoV steel. Keywords: steel, structure, hardness, wear resistance, isothermal hardening, cryogenic treatment.