Tribological behavior of 316L stainless steel reinforced with CuCoBe + diamond composites by laser sintering and hot pressing: a comparative statistical study

The aim of this work was to perform a statistical analysis in order to assess how the tribological properties of a laser textured 316L stainless steel reinforced with CuCoBe - diamond composites are affected by diamond particles size, type of technology (laser sintering and hot pressing) and time of tribological test. The analysis started with the description of all response variables. Then, by using IBM® SPSS software, the Friedman’s test was used to compare how the coefficient of friction varied among samples in five-time points. From this test, results showed that there was no statistically significant difference in the coefficient of friction mean values over the selected time points. Then, the two-samples Kolmogorov-Smirnov (K-S) test was used to test the effect of the diamond particles size and the type of technology on the mean of the coefficient of friction over time. The results showed that, for both sintering techniques, the size of the diamond particles significantly affected the values of the coefficient of friction, whereas no statistical differences were found between the tested sintering techniques. Also, the two-way ANOVA test was used to evaluate how these factors influence the specific wear rate, which conducted to the same conclusions drawn for the previous test. The main conclusion was that the coefficient of friction and the specific wear rate were statistically affected by the diamond particles size, but not by the sintering techniques used in this work.This work was supported by FCT national funds, under the national support to R&D units grant, through the reference projects UIDB/04436/2020 and UIDP/04436/2020. Additionally, this work was supported by FCT with the reference projects UIDB/00319/2020 and PTDC/CTM-COM/30416/2017

Effect of Sintering Temperature and Cooling Rate on the Microstructure and Hardness of Fe-Cr-Mo-V-W-C Sintered Steel added with MoS₂

Abstract In this work, the Fe-Cr-Mo-V-W-C sintered steels added with MoS2 (1, 3 and 5 wt.%) were produced by powder metallurgy process. The specimens were prepared by mixing, compacting and sintering at temperatures of 1150, 1200 and 1250°C for 45 min in vacuum furnace. After sintering, the specimens were cooled down with N2 at the different cooling rate (0.1 and 5.2°C/s). The density, hardness and microstructure of the sintered Fe-Cr-Mo-V-W-C steels were investigated. The experimental results indicated that the density and hardness of sintered steel could be improved by increase MoS2 addition, cooling rate and sintering temperature. The sintering mechanism was varied from solid state sintering to liquid phase sintering depend on sintering temperatures and MoS2 content. The presence of liquid phases and the increasing of cooling rate resulted in the amount of carbide precipitated decreased in the steel grain but increased precipitation at grain boundaries. The solidified of liquid and eutectic phases were found rising by increased cooling rate. Carbide precipitation in steel grain could be improved by added MoS2 and sintered at low temperature. From the results, it was indicated that the addition of MoS2, increase sintering temperature and cooling rate resulted in the precipitation of carbide, solidified liquid and eutectic phases, and grain growth in the sintered Fe-Cr-Mo-V-W-C steel.</jats:p

Study of bladder release agent formulas and methods to evaluate their efficiencies by using reciprocating tribometer

Abstract Bladder is one of the most important components in tire manufacturing process. In tire industry, methods to prolong bladder service-life and good bladder coatings for non-stick surface has been acquired. Bladder coated with good release agents can help reducing nonconforming products and increasing production efficiency. In this work, semi-permanent release agent formulas were studied. A new method to evaluate release agent efficiency by using a reciprocating tribometer were also carried out. Polydimethyl siloxane (PDMS) release agent formulas were developed with and without polymethyl hydrogen siloxane (PMHS). Effects of metal salt cure catalyst were also studied. In this work, method of release efficiency test was developed by using a reciprocating tribometer according to ASTM G133-05. It can be used to determine coefficient of friction of the coated surface and durability of the coatings. Coating durability test was also confirmed by repeating compression molding test to determine the number of release cycles. It was found that film durability was improved by adding the metal salt catalyst and PMHS. As the PMHS loading was increased, film endurance was improved to an optimum loading. Friction coefficient of the coatings could be related to the mold release ability and durability of the release agents. The technique can be used to estimate the service-life of the coated bladders. It can be used as a guideline for development of mold release agents in tire manufacturing industry.</jats:p

Thermal and Melting track Simulations of Laser Powder Bed Fusion (L-PBF)

Abstract Laser powder bed fusion (L-PBF) process involves with the construction of phase transformation, melting, and rapid solidification of weld metal powder bed which affects the properties and the microstructure of final parts, e.g. density, dimension, mechanical properties, void, porosity, and non-fully melted particle. The aims of this work were to study the effect of process parameters, e.g. laser power and scanning speed, on the temperature field and melt pool geometry and the characteristics of single melting track in the L-PBF process by using the commercial CFD software simulation Flow-3D (Flow-weld). The laser power, scanning speed, laser spot diameter, and layer thickness varied in this study were 120 W, 140 W, 0.4 m/s, 0.6 m/s, 0.8 m/s, 80 μm and 50 μm respectively. The results stated that at the lower scanning speed, the temperature field has a region of heat distribution larger than that of the higher one. The geometry of melt pools can be changed from ellipse shape to tear drop shape when the scanning speed is increased. The width and depth of laser melting track is increased when the higher laser power and lower scanning speed are applied. The void is found underneath the laser melting track when the scanning speed changes from 0.4 m/s to 0.6 m/s.</jats:p