The plasma nitriding of tool steel under atmospheric-pressure was performed using a dielectric barrier discharge method, resulting in the formation of a uniform nitrided layer. In this study, the tribology properties of the nitrided layer generated by atmospheric-pressure plasma nitriding were investigated. The results showed that the surface hardness of the tool steel nitrided by the atmospheric-pressure plasma method were increased by more than twofold compared with that of the core material. The surface hardness and the thickness of the nitrided layer were uniform, with values of 1300 HV and 30 μm, respectively. In addition, the wear rate of the sample nitrided by the atmospheric-pressure plasma method was decreased by more than 25 times compared with that of the untreated sample. Only the emission of the N2 second positive system and Ar were detected by the optical emission spectroscopic observation of the generated plasma. For this reason, we consider that the nitriding of this research caused by the dissociation of nonexcited N2, NH3, NH2, and NH etc. on the sample like a gas nitriding.
The transportation of a colossus painted in the ancient Egyptian tomb of Djehutihotep (Dayr al-Barsha) is known as an example of lubrication application. However the benefits and the nature of lubrication used by ancient Egyptians are controversial. In order to clarify this issue, the physical parameters involved in the transportation are carefully reviewed. The traction force is a key parameter, and is evaluated by simple physical models and the results of biomechanical and ergonomic studies. The results of this work suggest high traction force can be produced only with an excellent team coordination, and the friction coefficient between sledge and ground is efficiently reduced by hypothetical methods which exclude probably wood-on-wood or wood-on-sand surface contacts.
This paper theoretically presents the comparative performances of conical hybrid journal bearing with 4-pockets and 6-pockets compensated with constant flow valve (CFV) under micropolar fluid lubrication for various semi-cone angles. The numerical solution of the modified Reynolds equation for micropolar fluid flow on the conical surface has been done by using finite element method using Galerkin’s technique along with the necessary boundary conditions and iterative scheme. The bearing performances have been presented for two different semi-cone angles, radial load and the restrictor design parameter. It is observed that bearing performances improve for 6-pockets CFV than 4-pockets. The bearing performances also increase with increase in semi-cone angle, constant flow valve restrictor and micropolar parameters significantly. With increase in semi-cone angle of bearing the direct stiffness, damping coefficients and the stability have been observed to increase under micropolar lubrication for 6-pockets CFV restrictors.
Centrifugal casting process was applied for fabricating the functionally graded Aluminium/10% AlB2 composite under the centrifuging speed of 1200 rpm and hollow cylindrical (150 × 150 × 15 mm) component has been obtained. The outer, middle and inner surfaces of the FGM those were at the distance of 1 mm, 8 mm and 15 mm from the outer periphery were taken for three body abrasive wear test and the applied load was varied (33 N to 80 N) on these surfaces in the presence of silica sand and alumina as abrasive mediums. The wear test results showed that increase in load and increase in distance from the outer periphery of the FGM increases the wear rate. The surfaces of the FGM abraded with silica sand displays higher wear rate than the surfaces abraded through alumina. SEM analysis has been performed on the surfaces abraded by both medium and it was observed that severity of wear was less in the presence of alumina as abrasive medium during the abrasion test.
The effects of counterface surface roughness on the friction and wear behaviors of polyether ether ketone (PEEK) are studied using blocks on a ring wear tester under oil-lubricated conditions. The blocks are made of unfilled PEEK and a PEEK composite that is 30 wt% carbon fiber. The ring is made of forged steel (SF540A) and its surface roughness varies between 0.04 to 1.86 μm Ra; the sliding velocity and load are 10.2 m/s and 588 N, respectively. Results indicate that both the friction coefficient and each block’s specific wear rate increase from low to high values when the ring’s surface roughness exceeds a certain value (0.2–0.4 μm Ra). In high friction and wear regions, significant differences exist in the friction and wear behaviors of both PEEK and the PEEK composite. The PEEK composite shows a significantly lower friction coefficient and wear rate as compared to PEEK. However, the PEEK composite causes greater wear of the ring, though the extent to which the ring wears is dependent on the ring’s surface roughness. Wear particles and wear scars on both materials are observed and analyzed using a scanning electron microscope and an energy-dispersive X-ray spectroscope. The wear mechanisms are then discussed.