Papers by Author: Hong Yu Wang

Abstract: In order to improve the surface wear-resistance and overall shock-resistance of 65Mn steel, effects of rare earth (RE) particle size, adding amount and boronizing time subjected to quenching and medium-temperature tempering treatment were studied systematically. Optimizing basic component of low-temperature boronizing reagent and RE types, the depth of boronizing layer was selected as main evaluation parameter through the orthogonal test of RE-boronizing. Experimental results show that, cerium oxide with particle size of 20nm and content of 4% has the best effect of accelerating boronizing process on 65Mn steel at 700°C for 9 h, and the depth of boronizing layer with RE-boronizing is about 3.3 times than without adding RE; meanwhile, the heart of 65Mn steel still keeps good strength and toughness due to temper troostite microstructure. It can be concluded that the strengthening and toughening treatment of low-temperature RE-boronizing can obtain hard-surface and tough-core properties on 65Mn steel.

Abstract: The characteristics of open CNC system and the current several open CNC system models are introduced in this paper. In order to overcome the contradiction between the frequent changes demand and the closure of the traditional system, the open CNC system software and hardware architectures were investigated based on web-collaborative design and development, which improve the system development efficiency. Using the Windows XP operating system as a software platform, the Visual C++ 6.0 object-oriented programming language is adopted to design the CNC drilling control software based on the "PC + NC" the model and modular co-design methods, which improve the openness of the CNC system.

Abstract: In the process of modeling the squashed piece of powders for the simulation of the temperature field of laser cladding, the metallurgical model and the pore model were proposed separately. The effects of the organizational form, the contact resistance and the thickness of the squashed piece of powders on the temperature were considered. Different values of physical parameters of the squashed piece of powders were converted, different contact resistances were calculated and the laser absorptivity for different process parameters of laser cladding was determined. The temperature curves of six typical nodes and the temperature gradient of two nodes in the molten pool of the substrate were discussed from different aspects.

Abstract: Three NiCoCrAlY coatings strengthened by different contents of nano-SiCp (nanometric SiC particles)were prepared on Ni-based superalloy substrates using crosscurrent CO2 laser, and the thermal shock test of these coatings was conducted by cycling between 1050°C and room temperature (10-15°C). The spalled area in the oxide scale of coatings after 10 thermal shock cycles and the thermal shock cracks in the cross-section of coatings after 100 thermal shock cycles were investigated using SEM, OM, and other means. The results show that the thermal shock resistances of NiCoCrAlY coatings are improved after adding nano-SiCp. Among nano-SiCp-added coatings, the coating added with 1.0 wt% nano-SiCp performs best. After 10 thermal shock cycles, there is a slight spallation whose area is only 2.65% in the oxide scale of the coating; after 100 thermal shock cycles, no internal crack is observed in the cross-section, and the amount and size of propagating cracks are slight.

Abstract: NiCoCrAlY coatings strengthened by different content of nano-Al2O3p, using crosscurrent CO2 laser, were prepared on Ni-based superalloy substrates, and thermal shock behaviors of these coatings were investigated by cycling between 1050°C and room temperature (forced water quenching).The results show that the thermal shock resistances of nano-Al2O3p-added coatings are definitely better than that without adding nano-Al2O3p. Among the nano-Al2O3p-added coatings, the coating added with 0.5wt% nano-Al2O3p performs best. After 10 thermal shock cycles, the spalled and spalling area in the oxide scale of the no-nano-Al2O3p coating reaches up to 27.7%, and the main failure form of the oxide scale is an expanding unit-spalling type in thermal shock cycles. While the area in the oxide scale of nano-Al2O3p-added coatings is only 10%~60% to the no-nano-Al2O3p one, and the failure of these oxide scales is mainly in the form of unit-spalling type. After 100 thermal shock cycles, many cracks turn up in the cross-section of the no-nano-Al2O3p coating, including propagating crack and internal crack. While no internal crack appeared in nano-Al2O3p-added coatings, and the propagating cracks are smaller than no-nano-Al2O3p one.

Abstract: The green presetting of powders was performed on the substrate by introducing a novel technique namely squash presetting method, and cladding coatings were prepared by crosscurrent CO2 laser in this work. Based on the concept of laser energy efficiency which being accepted generally by insider, the energy efficiency of squash presetting laser cladding was determined. Meanwhile, effects of processing parameters including specific energy, laser power, scanning speed and spot diameter on energy efficiency were investigated through an orthogonal test. The results show that the energy efficiency increases at first and then decreases with the increase of specific energy, and the energy efficiency is relatively higher when laser specific energy ranged from 90 J/mm2 to100 J/mm2. Among three single-factors, the effects of spot diameter on energy efficiency are most significant, laser power takes second place, and scanning speed comes next. It is considered through analysis that the relationship between energy efficiency and processing parameters is closely related to powders melting and heat-conduction course of squash presetting laser cladding.

Abstract: The compound of micron powders and nanometer powders is a magnificent step in the application and development of metal matrix composite reinforced by nanometer particles. By taking nano-Al2O3 powders and Ni-based micron powders as the research object, the preparation process of metal matrix micro/nano-powders reinforced by nanometer particles with high energy ball-milling is discussed from three aspects: the additive process of nanometer powders, the additive content of nanometer powders, and the required ball-milling time in the paper. The results show that the additive process of nanometer powders which uses directly the dispersed uniformly nanometer suspensions as grinding medium can effectively decrease and avoid nanometer powders’ agglomeration of composite powders. Nanometer particles are well distributed in the composite powders. The optimum additive content of nanometer powders is consistent with the theoretical model of mixture ratio, which is determined by the ratio of the average diameter of micron powders and nanometer powders and their density of corresponding solid materials. Meanwhile, the required ball-milling time for preparation of better uniformity composite powders is no more than 0.5hr. This implies that the preparation process has a high productivity. Moreover, the preparation process is verified through other nanometer powders including nano-SiC powders and nano-CeO2 powders.