Sithipong Mahathanabodee

Effects of Cooling Rate and Carbon Content on Mechanical Property of Sintered Fe-Cr-Mo Alloys

Advanced high strength steel (AHSS) was prepared using the conventional ‘press and sinter’ process.The compacts of ultralow carbon Fe-Cr-Mo powder with carbon additions (base metal powder admixed with 0.1,0.2 and 0.3 wt.% graphite) and without carbon addition (plain base powder) were sintered in a vacuum furnace at pressure of 1.28 x 10-5MPa at 1280 °C for 45 min. After sintering, the sintered specimens were continuously cooled with different nitrogen gas pressures of 0, 2500 and 5000 mbars (or 0, 0.25, 0.5 MPa). Mechanical properties of the sintered alloys were strongly controlled by carbon contents and cooling rates after sintering. The sintered specimens, with 0.3 wt.% carbon and cooled by nitrogen of 5000 mbars, showing superior tensile strengths and good ductility, had microstructures dominated by carbide-free bainitic structures and some retained austenite. The sintered specimens with lower carbon contents and cooled under slower cooling rates, having lower tensile strengths but slightly higher ductility, had microstructures with lower bainite volume fractions and even without bainitic structures. The dominant phase in the sintered specimens with low strength but high ductility was ferrite.

Comparative Studies on Wear Behaviour of Sintered 316L Stainless Steels Loaded with h-BN and MoS2

Mechanical properties and wear behavior of stainless steel embedded with different solid lubricants were investigated. Hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2)-embedded 316L stainless steels (SS316L/h-BN and SS316L/MoS2) were prepared by powder metallurgy method. Various h-BN and MoS2 contents (10, 15 and 20 vol%) were mixed with 316L stainless steel powders and then sintered at 1200°C in H2 atmosphere for 60 min. The experimental results showed that small boride phase and h-BN powder occupied the pores in the microstructure of SS316L/h-BN composite whereas the MoS2 second phase occupied the pores of the sintered 316L matrix in the microstructure of SS316L/MoS2 composite. The addition of h-BN decreased the sintered density and hardness whereas that of MoS2 gave the opposite effect. Dry sliding wear behavior of composites was investigated by using pin-on-disc test rig at the sliding speeds of 0.1 and 0.2 m/s and the applied load of 3 N. The results showed that the MoS2 composites had higher wear resistance than the h-BN composite but the h-BN composite yielded a better friction reduction.

Effect of h-BN Content on the Sintering of SS316L/h-BN Composites

In this work, the three compositions of hexagonal boron nitride (10, 15 and 20 vol. %)-embedded 316L stainless steel (SS316L/h-BN) composites were prepared by a conventional powder metallurgy technique and then sintered at varying temperatures of 1100 to 1250°C for 60 min in H2 atmosphere. The h-BN content and sintering temperature were found to affect the microstructure and hardness of the composites. The hardness decreased with increasing h-BN content and was improved by increasing the sintering temperature. Microstructure results revealed that the boride phase was formed at the grain boundary at the sintering temperature higher than 1150°C and the boride phase formation was observed to transform the h-BN in the composites.

Tribological properties of carbon nanotube as co-reinforcing additive in carbon black/acrylonitrile butadiene rubber composites for hydraulic seal applications

This work investigated the cure characteristic, physical mechanical properties, and tribology behavior of carbon black filled acrylonitrile butadiene rubber composites using multi-walled carbon nanotubes as co-reinforcing additive in various contents from 0, 3, 6, 9, and 15 parts per hundred rubbers. The physical and tribological behavior was also observed in large-scale piston driven hydraulic apparatus which was specially designed for seal applications. The results suggested that the modulus and hardness were found to increase after adding multi-walled carbon nanotube whereas the tensile and tear strength were not significantly affected. Adding multi-walled carbon nanotube was found to increase the bound rubber and crosslink density. For ball-on-disc tribo-testing, it was found that the coefficient of friction of the rubber composites decreased with multi-walled carbon nanotube content and the applied loads whereas the specific wear rate was more influenced by the applied loads used. Finally, under the large-scale piston driven hydraulic test apparatus in comparison with commercial grade rubber seals, it was found that the weight loss for the acrylonitrile butadiene rubber composites with multi-walled carbon nanotube was much lower than that without multi-walled carbon nanotube. The carbon black/acrylonitrile butadiene rubber composites with 9–12 parts per hundred rubbers multi-walled carbon nanotube were recommended as the most suitable for hydraulic seal applications.