Effect of Chromium on Microstructure and Oxidation Wear Behavior of High-Boron High-Speed Steel at Elevated Temperatures

In order to investigate the effect of Cr content on the microstructures and oxidation wear properties of high-boron high-speed steel (HBHSS), so as to explore oxidation wear resistant materials (e.g., hot rollers), a scanning electron microscope, an X-ray diffractometer, an electron probe X-ray microanalysis and an oxidation wear test at elevated temperatures were employed to investigate worn surfaces and worn layers. The results showed that the addition of Cr resulted in the transformation of martensite into ferrite and pearlite, while the size of the grid morphology of borides in HBHSSs was refined. After oxidation wear, oxide scales were formed and the high-temperature oxidation wear resistance of HBHSSs was gradually improved with increased additions of Cr. Meanwhile, an interaction between temperature and load in HBHSSs during oxidation wear occurred, and the temperature had more influence on the oxidation wear properties of HBHSSs. SEM observations indicated that a uniform and compact oxide film of HBHSSs in the worn surface at elevated temperatures was generated on the worn surface, and the addition of Cr also reduced the thickness of oxides and inhibited the spallation of worn layers, which was attributed to improvements in microhardness and oxidation resistance of the matrix in HBHSSs. A synergistic effect of temperature and load in HBHSSs with various Cr additions may dominate the oxidation wear process and the formation and spallation of oxide films.

Justification for using resourcesaving banding technology in renovative production

The article substantiates the expediency of applying the basics of resource saving in the development of innovative technologies for strengthening serial parts and restoring worn ones. At the same time, the main task is the rational use of available material resources in the conditions of a decline in production, when it becomes profitable to restore metal-intensive parts worn out to a critical level. In capital repair of machines, the main problems are associated with the energy intensity of the process and a significant number of rejected parts that cannot be restored. Currently, most of the worn-out metal-intensive cast iron and steel body parts that have exhausted the resource are subjected to energy-intensive melting. For the reuse of metal-consuming parts in operation, a technology has been proposed for multilayer banding of a worn surface, in which steel tape is used instead of traditional banding rings. Winding the tape occurs under an interference in several layers. In this case, a multilayer bandage with interturn stresses is formed, which is not inferior in strength to a whole banding ring. The use of a steel “bandage” for the “treatment” of parts reduces the metal consumption for its manufacture by 2.5 times in comparison with the well-known one-piece ring made of round steel. As an example, the article substantiates the possibility of carrying out the banding process in relation to the restoration and strengthening of the seat under the bearing of the housing part. A multilayer bandage can also be used in the recovery of metal-intensive rolling rolls written off in scrap used on broadband cold rolling mills.

Optimization and Nanoreinforcements of Lubricant Concentration for Steel Sheet Forming Process

In metal-mechanic industry, lubricants are applied to improve products’ quality and tools useful life, while reducing friction and wear, also removing the generated heat during the material processing. Tribological evaluations are performed varying the water content of two widely used lubricants in automotive metal-forming operations. Evaluations are first performed to determine the optimal lubricant dilutions, followed by reinforcement of 2D-nanostructures of hexagonal Boron Nitride (h-BN). Tribological characterization under extreme pressures (EP) are performed with a four-ball tribometer according to the Institute for Sustainable Technologies –National Research Institute (ITeE-PIB) Polish method under scuffing conditions. The optimized concentrations are determined for Ecodraw and Montgomery lubricants, representing a 28% and 3% improvement in pressure loss limit at 1:8 and 1:6 concentrations, respectively. Block-on-ring tribotest is used to determine the coefficient of friction (COF) of the optimized lubricant dilutions and h-BN nanolubricants, which represent ~10% improvement. These results could be attributed to diverse factors such as a layering mechanism of the 2D nanostructures, soft van der Waals forces between 2D h-BN layers, and the deposition of h-BN on the worn surface, decreasing the shearing stress and COF. Finally, thermal conductivity evaluations showed an enhancement by 30% and 15% with addition of h-BN, demonstrating the potential of 2D nanostructures for improving the efficiency on antiwear and thermal transport.

Wear Characteristics of 22MnB5 Boron Steel under Friction Micro Pin-on-Disks Test

22MnB5 Boron Steel can be considered as emerged material for high strength and low weight application. This material potentially used in abrasive condition such as cutting tool or brake pad where high friction resistance applies. In this study, the wear characteristics of 22MnB5 was investigated under the frictional tests via micro pin-on-disk. 22MnB5 Boron Steel was prepared the form of round shape within the size of 2.6 mm thickness and 12 mm diameter by using laser cutting. 4 different samples were tested namely blank (sample A), self-hardening heat treatment (sample B), 60 HRC hot stamped (sample C) and 70 HRC hot stamped (sample D). The results show that Coefficient of Friction (COF) increased as the hardness of 22MnB5 decreased. Low COF of 0.2114 recorded for sample D with 70 HRC hardness. The COF increased to 0.24, 0.29 and 0.3 when sample C (60 HRC), sample B (52 HRC) and sample A (45.5 HRC) applied respectively. For pin-on disc test, worn area decreased as the hardness increased. 22MnB5 that prepared with the highest hardness of 70 HRC presented smallest wear area of 700 µm x 2400 µm. It is followed by 800 µm x 2400 µm, 1000 µm x 2400 µm, 1600 µm x 2800 µm, when sample C, B and A were scratched. Observation on the worn surface revealed delamination of 22MnB5 surface in the form of fragmented flaking debris.

Synergistic Performance of Expanded Graphite – Mica amalgamation based Non-Asbestos Copper-Free Brake Friction Composites

Recent advancements in brake pad applications emphasise various friction compositions that exclude toxic components such as asbestos, copper etc., in order to provide superior performance without hurting the environment, human life and aquarium species. In this work, brake friction materials were fabricated by the conventional manufacturing process as standard brake pads using expanded graphite with the synergetic effect of thermal resistant material mica flakes. Six standard brake pads were produced based on varying the expanded graphite by 16, 14, 12, 8, 6 & 4 weight percentage, which is compensated using the Mica flakes by 4, 6, 8, 12, 14 & 16 weight percentage, fixing the composition of other ingredients and designated as BM01, BM02, BM03, BM04, BM05 and BM06. Physical, chemical and mechanical, characterisations of the formed friction materials were carried out in accordance with IS 2742 and ISO 6312. A full-scale inertia brake dynamometer was used to determine the fade, recovery characterisations with the pressure and speed sensitivity as of JASO-C-406. From the experimental observations, BM03 friction composites reveal excellent low fade and high recovery characteristics because of the integrated effect of expanded graphite (superior lubricity) & mica (good thermal stability). Worn surface analysis was studied with the help of a scanning electron microscope. The inclusion of expanded graphite-mica as a hybrid “lubricant-filler” combination in composite materials for friction braking application results in performance synergism.

Modeling the abrasive wear behavior of in-situ synthesized magnesium RZ5/TiB2 metal matrix composites

In the present study, the statistical analysis on tribological behavior of RZ5/TiB2 magnesium-based metal matrix composites is carried out using Taguchi design and analysis of variance (ANOVA) technique. Taguchi analysis using signal-to-noise ratio indicates that the sliding distance and wt.% TiB2 are the most significant factors in evaluating weight loss and coefficient of friction, respectively. The regression equation is formulated utilizing the ANOVA technique to study the output responses based on the input abrasive wear test experimental results. The regression equation is validated through a comprehensive study taking a series of abrasive wear tests and indicates the percentage deviation of regression modeling is in the range of ± 10%. The individual and combined effect of wear parameters on tribological behavior are investigated through the main effect plots and response surface plots. The micrograph of the worn surface of RZ5/TiB2 composites is studied using field emission scanning electron microscope (FESEM), indicating the formation of an oxide layer on the worn surface.

Tribo-oxide Competition and Oxide Layer Formation of Ti3SiC2/CaF2 Self-Lubricating Composites during the Friction Process in a Wide Temperature Range

Ti3SiC2/CaF2 composites were prepared by the spark plasma sintering (SPS) process. Both the microstructure of Ti3SiC2/CaF2 and the influence of test temperature on the tribological behavior of the Ti3SiC2/CaF2composites were investigated. The synergistic effect of friction and oxidation was evaluated by analyzing the worn surface morphology. The results showed that Ti3SiC2/CaF2 were still brittle materials after adding CaF2, which was in agreement with Ti3SiC2. The hardness, relative density, flexural strength and compressive strength of the Ti3SiC2/CaF2 composites were slightly lower than those of Ti3SiC2, and the addition of CaF2 decreased the decomposition temperature of Ti3SiC2 from 1350 to 1300 °C. Simultaneously, as the temperature of the test increased, the friction coefficient of Ti3SiC2/CaF2 showed a downward trend (from 0.81 to 0.34), and its the wear rate was insensitive.

Experimental study on two-body and three-body abrasive wear behaviour of jute-natural rubber flexible green composite

The use of laboratory testing has become more significant to assess abrasion resistance in flexible reinforcement of armour and car structural components. In this study, compliant composite with constituents as woven jute fabric and natural rubber (NR) encapsulated in an NR-based B stage cured prepreg were tested for wear due to abrasion under two- and three-body conditions. Flexible composites are fabricated in three different configurations namely Jute/Rubber/Jute (JRJ), Jute/Rubber/Rubber/Jute (JRRJ) and Jute/Rubber/Jute/Rubber/Jute (JRJRJ). The present study makes use of abrasive paper with a grit size of 60 and silica sand with size 250 µm as the abrasive medium for two- and three-body abrasion tests respectively and the specific rate of wear is calculated. Though the wear trend of the composites follows a similar pattern in the case of two- and three-body wear, the mechanisms governing the wear are found to be different. The morphology of the worn surface is studied with the aid of a scanning electron microscope.

Tribological behaviour of lamb bone ash and boron carbide reinforced ZA-27 hybrid metal matrix composites under dry sliding conditions

This study aims to investigate the tribological behaviour of lamb bone ash (LBA) and boron carbide (B4C) reinforced ZA-27 hybrid metal matrix composites fabricated using a stir casting process. The weight percentage of LBA and B4C particles in the composites were varied from 0-5 wt.%. The composites have been evaluated for density, porosity and microhardness before tribological testing. Dry sliding friction and wear behaviour of composites were studied on a pin-on-disc tribometer by varying load from 10-50 N at a fixed sliding speed of 1 m/s. Also, to investigate the effect of sliding speed on friction and wear behaviour of composites, tests were carried out at 2 m/s and 3 m/s of sliding speed. A scanning electron microscope (SEM) was used for examining the microstructure and worn surface morphology of composite samples. SEM micrographs revealed the presence and homogeneous distribution of reinforcement particles, and energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the presence of LBA and B4C particles in the composites. Composites density decreased, and porosity increased with the addition of reinforcement particles. The microhardness of the 5 wt.% reinforced LBA composite improved by 18.38%, whereas hybrid composite containing (2.5 wt.% LBA + 2.5 wt.% B4C) showed an improvement of 42% compared to the base alloy. The coefficient of friction (COF) and wear loss increased with the increase in load, whereas COF decreased and wear loss increased with the increase in sliding speed. Composites showed superior wear resistance even at higher loads and sliding speeds. SEM micrographs of worn surface revealed adhesion and abrasion type of wear mechanisms. Therefore, with the improvement in wear resistance this developed composite can be used as a bearing material over monolithic ZA-27 alloy in the automotive sector.