24CrNiMo alloy steel samples for preparing the brake disc of high-speed train were fabricated by direct laser deposition (DLD) with different laser energy area density (EAD). The effect of various energy area densities on the distribution, size and mechanism of pores, slag inclusions and cracks in the DLD 24CrNiMo alloy deposition layer were investigated. The results show that the increase of the EAD leads to the increase of the dilution index and area of the molten pool. The density of multilayer samples reached highest (99.25%) when the EAD was 100 J/mm2. The morphology of pores had irregular deformation when the EAD was low while had smooth sphere morphology when the EAD was high. The cracks ratio increased with the increase of the EAD while the content of inclusion defects decreased. A behavioural process for the re-melting of pore defects at different energy densities was discussed, and the formation of inclusion defects with low EAD was studied to illuminate the EAD effects on defects. The samples deposited at the 100 J/mm2 have no obvious defects and relatively high density, this EAD can be considered as a reference to prepare 24CrNiMo samples with low defects by DLD.

Effect of laser energy density on defects behavior of direct laser depositing 24CrNiMo alloy steel

The extensive tribological use of nodular cast iron in ground transport industry, e.g., trains and automobiles, has brought growing scientific interest. The various applications of this material are due to the versatility of mechanical properties without adding alloy elements, making possible to achieve good results varying just the heat treatment. Due to its high fluidity, workpieces made of this material can be produced with final dimensions and shapes very close to the designed ones, making necessary just the use of finishing machining operations to get the final dimensions, more specifically those concerning the grinding process. To optimize cost production, machining processes became the focus of scientists and engineers. The grinding wheel can determine the success of an operation as its properties influence productivity and workpiece quality decisively. This work analyzes the grinding process of the ductile iron GGG-70 (average hardness of 270 HB) using two types of vitrified bonded CBN grinding wheels, which have as their only distinction the marked difference in friability of the abrasive grains. The performance of each grinding wheel will be analyzed taking into account the output parameters values obtained from surface roughness, average power, diametric wear of the grinding wheel, microstructure of the ground surfaces, and microhardness measures from the ground surface to the center of the workpiece. It was observed that the less friable wheel produced, regarding the average surface roughness, values of 0.27, 0.30, and 0.36 μm for the feed rates of 0.5, 1.0, and 1.5 mm/min, respectively, and, regarding the diametric wheel wear, produced values of 2.52, 2.99, and 4.01 μm for the same feed rates, respectively. On the other hand, when using the more friable wheel, average surface roughness values of 0.33, 0.44, and 0.64 μm and diametric wheel wear values of 3.21, 4.22, and 7.24 μm were obtained. In this way, the less friable wheel showed better results for all the conditions. Considering the feed rate order of 0.5, 1.0, and 1.5 mm/min, the improvement in surface roughness was about 18.18, 31.82, and 43.75%, respectively, and the reduction of the wheel wear was about 21.50, 29.15, and 44.61%.

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Comparative analysis of two CBN grinding wheels performance in nodular cast iron plunge grinding

Effect of different strengthening methods on rolling/sliding wear of ferrite–pearlite steel

In this paper, low-temperature plasma nitriding at 550 °C for 4 h was performed on a pure titanium sample with nanostructured surface layer induced by surface mechanical attrition treatment (SMAT). Microstructure, surface topography, surface mechanical properties and in vitro biocompatibility of SMAT nitrided titanium sample were investigated in comparison with those of original and SMATed samples. Experimental results revealed that a nanostructured nitrides layer was fabricated on the surface of SMAT nitrided titanium sample, leading to enhance the surface hardness and to reduce wear volume. Additionally, the surface roughness and wettability of SMAT nitrided sample are different from those of the original and SMATed samples. Furthermore, the SMAT nitrided sample exhibits promoted cell attachment, proliferation and differentiation compared to those of the original and SMATed samples. The enhanced cell response on SMAT nitrided sample may be originated from its unique surface characteristics, such as surface “nano-effect”, formation of titanium nitrides and enhanced wettability, etc. This composite surface treatment may provide a promising method to improve surface mechanical properties and in vitro response of titanium implants simultaneously.

Simultaneously improving surface mechanical properties and in vitro biocompatibility of pure titanium via surface mechanical attrition treatment combined with low-temperature plasma nitriding

The wheel-rail contact is an open system contact, which is subjected to various environmental conditions, such as temperature, humidity, water, and even leaves. All these environmental factors influence wheel-rail wear. Classical wheel-rail wear has been extensively studied under dry and clean conditions previously. However, with changes in environmental conditions, the wear rate and wear mechanism can change. This paper reviews recent contributions to wheel-rail wear with a special focus on the influence of environmental conditions. The main part includes the basics of wheel-rail wear, experimental methodology, wear and rolling contact fatigue (RCF), and some measures to counter these degradation mechanisms.

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A Review on Wear Between Railway Wheels and Rails Under Environmental Conditions

Optimization of strength and toughness of railway wheel steel by alloy design

Investigation on rolling contact fatigue of railway wheel steel with surface defect

Influence of solid solution strengthening on spalling behavior of railway wheel steel

Influence of a hybrid treatment consisting of fine particle bombardment and powder impact plating on the scuffing behavior of ductile cast iron

The occurrence of scuffing is widely observed on tribological components made of Al-Si alloys. The object of this study is to investigate the scuffing behavior of Al-Si alloy modified by fine particle bombarding (FPB) and powder impact plating (PIP) hybrid surface treatment. FPB treatment, PIP treatment, and hybrid treatment consisting of FPB and PIP were conducted on Al-Si alloy samples. The surface morphology, microstructure, and hardness of the samples were examined. Block-on-ring tests were performed to investigate the scuffing resistance of the samples. The test results show that the scuffing resistance of Al-Si alloy depends on the surface hardness and friction coefficient. Scuffing resistance is improved by FPB treatment, which increases the surface hardness by nanocrystallization and reduces the friction coefficient by decreasing the surface roughness and producing a microdimpled surface. PIP treatment reduces the friction coefficient by generating an Sn coating on the surface of the sampl...

Yanhua Gong

Papers

Optimization of strength and toughness of railway wheel steel by alloy design

Investigation on rolling contact fatigue of railway wheel steel with surface defect

Influence of solid solution strengthening on spalling behavior of railway wheel steel

Influence of a hybrid treatment consisting of fine particle bombardment and powder impact plating on the scuffing behavior of ductile cast iron

Scuffing Behavior of Al-Si Alloy Modified by Fine Particle Bombarding and Powder Impact Plating Hybrid Surface Treatment