Kamran Amini

Effect of deep cryogenic treatment on the formation of nano-sized carbides and the wear behavior of D2 tool steel

The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), hardness test, pin-on-disk wear test, and the reciprocating pin-on-flat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.

Effect of deep cryogenic treatment on the properties of 80CrMo12 5 tool steel

The effect of deep cryogenic treatment on the mechanical properties of 80CrMo12 5 tool steel was investigated. Moreover, the effects of stabilization (holding at room temperature for some periods before deep cryogenic treatment) and tempering before deep cryogenic treatment were studied. The results show that deep cryogenic treatment can eliminate the retained austenite, making a better carbide distribution and a higher carbide amount. As a result, a remarkable improvement in wear resistance of cryogenically treated specimens is observed. Moreover, the ultimate tensile strength increases, and the toughness of the sample decreases. It is also found that both stabilization and tempering before deep cryogenic treatment decrease the wear resistance, hardness, and carbides homogeneity compared to the deep cryogenically treated samples. It is concluded that deep cryogenic treatment should be performed without any delay on samples after quenching to reach the highest wear resistance and hardness.

Effect of Deep Cryogenic Heat Treatment on the Wear Behavior of Carburized DIN 1.7131 Grade Steel

The effects of the deep cryogenic heat treatment on the microstructural changes, wear resistance, and hardness of carburized DIN 1.7131 grade steel were investigated. Results show that cryogenic heat treatment reduced the retained austenite and increased the carbide amount. In addition, after the cryogenic heat treatment, carbide shows a more uniform distribution, as compared to the conventionally treated ones. It was also clarified that the hardness of the cryogenically treated samples was improved, but the relative improvement decreases with the distance as the surface increases. It has been shown that the wear resistance improves due to the cryogenic heat treatment, and the predominant wear mechanism is a combination of the adhesive and tribo-chemical wear.

Erratum to: Investigation of the Effect of Heat Treatment on the Mechanical Properties and Microstructure of DIN 1.4057 Martensitic Stainless Steel

The effect of the temperatures of austenization and tempering on the microstructure and mechanical properties of martensitic stainless steel DIN 1.4057 (0.17% C, 15% Cr) is studied. An optimum combination of tensile strength and impact toughness is attained in the case of two-stage austenization (1030 and 970°C) with tempering at 200°C between the primary and secondary austenization. The carbides segregated during the tempering lower the growth of grains in the stage of the low-temperature austenization.

Cryogenic heat treatment — a review of the current state

The deep cryogenic heat treatment is an old and effective heat treatment, performed on steels and cast irons to improve the wear resistance and hardness. This process includes cooling down to the liquid nitrogen temperature, holding the samples at that temperature and heating at the room temperature. The benefits of this process are significant on the ferrous materials, but recently some studies focused on other nonferrous materials. This study attempts to clarify the different behavior of some materials subjected to the deep cryogenic heat treatment, as well as explaining the common theories about the effect of the cryogenic heat treatment on these materials. Results showed that polymers exhibit different behavior regarding to their crystallinity, however the magnesium alloys, titanium alloys and tungsten carbide show a noticeable improvement after the deep cryogenic heat treatment due to their crystal structure.

Effect of Carbide Distribution on Corrosion Behavior of the Deep Cryogenically Treated 1.2080 Steel

AbstractDeep cryogenic heat treatment is a supplementary process performed on steels specifically tool steels before tempering to improve the wear resistance and hardness of these materials. The carbide distribution changes via the electric current flow or the application of a magnetic field during the deep cryogenic heat treatment. Hence, the electric current and the magnetic field were applied to the samples to investigate the corrosion behavior of the deep cryogenically treated samples by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The results showed that increasing the carbide percentage and achieving a more homogenous carbide distribution during the deep cryogenic heat treatment will remarkably decrease the corrosion resistance due to a decrease in the solutionized chromium atoms in the structure as well as the increase in the martensite-carbide grain boundaries (the galvanic cell areas). Moreover, it was clarified that the electric current flow and magnetic fields reduce the carbide percentage, which leads to an increase in the corrosion resistance of these samples in comparison with the deep cryogenically treated samples.

The effect of electrolyte temperature and sealing solution in anodizing operation on hardness and wear behavior of 7075 -T6 aluminum alloy

Anodic oxide coatings are applied on aluminum alloys in order to improve corrosion resistance and to increase hardness and wear resistance. In the current study, a hard anodic coating was applied on AA7075-T6 aluminum alloy. To survey the anodizing temperature (electrolyte temperature) effect, three temperatures, namely, −5∘C, 0∘C and 5∘C were chosen and the samples were sealed in boiling water and sodium dichromate to study the role of sealing. For measuring the oxide coatings porosity and hardness and also for comparing the samples’ wear resistance field-emission scanning electron microscopy (FESEM), microhardness test and pin-on-disk method were utilized, respectively. The results showed that by increasing the anodizing temperature, hardness and consequently wear resistance decreased so that hardness and weight loss in the samples with no sealing decreased from 460HV and 0.61mg at −5∘C to 405 and 358HV and 1.05 and 1.12mg at 0∘C and 5∘C, respectively, which is due to the porosity increment by increasing the anodizing temperature. Also, sealing in boiling water and dichromate contributed to soft phases and coating hydration, which resulted in a decrease in hardness and wear resistance. Hardness and weight loss in the coated samples at −5∘C decreased from 460HV and 0.61mg in the samples with no sealing to 435 and 417HV and 0.72 and 0.83mg in the samples sealed in boiling water and dichromate, respectively.

Creation of Ni-B/Ni-P electroless coating on the WC particles without surface activator

One of the methods for improving metal-ceramic interface and suppression of agglomeration is the formation of a monolayer electroless coating on the particles. Investigations indicated that Ni-B monolayers should be first formed to develop in the next process an electroless Ni–P coating with the morphology of cauliflower. It was possible to produce a Ni-B layer on WC particles when a bath was heated at a temperature of 95 °C by using sodium borohydride and an appropriate stabilizer. Following this process, the Ni–P electroless coating was deposited on WC particles at 85 °C. In this way, two layers of electroless coating of Ni–B/Ni–P on the WC ceramic particles without using the surface activator were produced successfully. The coating morphology and surface analysis were performed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results showed that only the degreasing with acetone as a surface preparation of ceramic particles is sufficient to make a Ni–P or Ni–B coating. Electroless Ni–B coating with appropriate adhesion to the surface produces an acceptable surface for the electroless Ni – P coating formation.

Friction Stir Welding of Dissimilar Joints Between Commercially Pure Titanium Alloy and 7075 Aluminium Alloy

In this study, a joint between commercially pure titanium alloy and 7075 aluminium alloy was butt welded by using friction stir welding at a rotational speed of 1120 rpm and a traverse speed of 50 mmmin. The evaluation of hardness and microstructure was performed by using scanning electron microscopy. The phases in the weld area were identified by applying the X-ray diffraction technique and the Energy Dispersive X-ray Spectroscopy (EDS) analysis was used for the evaluation of intermetallic compounds of the weld area. The weld zone is cone-shaped and consists of aluminium and titanium particles that play an important role in increasing hardness and tensile strength. The weld area has three zones, namely the titanium base metal zone, the aluminium base metal zone, and the titanium-aluminium intermetallic compound mixed zone. It was also observed that the joint area on the aluminium side includes the stirred area, the thermo-mechanically affected zone, and the heat-affected zone, while the titanium joint area contains the stirred zone and the heat-affected zone. The hardness value of the weld area was around 360 HV, which means that in this area, compared to the base metal of titanium and aluminium, hardness has increased by 6% and 20%, respectively. This can be attributed to severe plastic deformation and formation of intermetallic compounds of titanium and aluminium in this area.