Advanced Materials Research Vols. 834-836

Abstract: In order to examine the influences of tungsten carbide particle size on decarburization behavior and microstructure of HVOF sprayed WC-Co coating, four kinds of agglomerated WC-12wt.%Co powders were deposited on mild steel substrates by using a high velocity oxy-fuel (HVOF) spray system. The phase compositions and microstructure of the feedstock powders and sprayed coatings were investigated by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), respectively. The results showed that the decarburization became more serious with the decreasing of tungsten carbide particle size in the starting powder. W phase was detected in the as-sprayed nanocomposite WC-12wt.%Co coating. All the coatings showed very compact microstructure with the hard phases embedded in Co matrix. The microstructure of HVOF sprayed WC-12wt.%Co coatings depended on the feedstock powder structure. The shape of tungsten carbide particles was rounder and the volume fraction of carbide phase decreased in coatings as the tungsten carbide particle size decreased.

Abstract: This dissertation employs the method of direct current (DC) magnetron sputtering on the reverse side of the high power LED aluminum substrate to deposit the AlN thin film. And then, we paste the high power LED beads to the front of the substrate, testing and studying the heat dissipation influences of the AlN thin film on the high-power LED beads. In order to compare easily, some parts of the reverse of aluminum substrate should be overlaid thermally conductive silicone. The result indicates that depositing the AIN thin film or the overlay thermally conductive silicone on the back side of the aluminum substrate can improve the heat dissipation capability of high power LED, the AIN thin film especially.

Abstract: Stellite 6 Co-based and Hӧganӓs Fe-based alloy coatings were deposited on austenitic engine valve using plasma transferred arc (PTA) hardfacing. The microstructures, composition distribution and mechanical properties of coatings were investigated by combining optical microscope (OM), scanning electron microcopy (SEM), field emission electron-probe analyzer (EPMA) and nanoindentation technique. The microstructures of hardfacing coatings consist of three phases which belong to hypoeutectic structure and Co-based coating has more uniformed and regularly changed microstructure. The determination of mechanical properties reveals that Co-based coating attains higher hardness value (~5.229 GPa), H/E (0.0265) and H³/E*² (0.00323) than that of Fe-based coating, signified better wear resistance property.

Abstract: 16Mn flanges cracked during producing.Physical and chemical analysis of the cracking 16Mn flange were performed,it was found that the chemical composite of 16Mn flange agreed well with standard NB/T 47008-2011,but the physical properties of it were abnormal,the sharpy values of which were far below standard requriemet.furthermore,the metallographic of the cracking 16Mn flange were bulky network polygonal ferrite and pearlite.And this was the main reason that caused the failure.And on the end some control motheds were suggested to this accident.

Abstract: TiAlLaN coatings were deposited on the cemented carbide substrates by mid-frequency magnetron sputtering system. The effects of Ar/N2 flow ratio on the composition, structure, adhesion and hardness followed with elastic modulus and H/E ratio were investigated systematically. Results indicate that all the Ti/Al ratios of the coatings were higher than that of the Ti/Al ratio in the target; however, the Ti/Al ratio increased with the Ar/N2 flow ratio changed. XRD patterns show that the intensity of (111) peak was elevated with the Ar/N2 flow ratio increased. Meanwhile, the peak shifted to lower angles, which implied increases of the lattice parameter. The TiAlLaN coating under the Ar/N2 flow ratio of 3:1 showed the best adhesion, the highest hardness and the lowest H/E ratio which indicated perfect wear resistance.

Abstract: In this paper, the thickness of the different layer of the multiple-layer homogeneous structure. is optimized designed on the condition that the absorption effort is the best Using the transfer matrix of sound pressure and particle velocity of each layer and the continuity condition at the interface between two lagers, the absorption coefficient of the multiple-layer homogeneous structure is deduced. According to the absorption coefficient, the thickness of different layer is optimized designed on the condition that the absorption effort is the best when the sound wave incident to the multiple-layer homogeneous structure with different frequency. In the last, an experiment is carried out, and the experiment results test the theoretical analysis is correct which can be applied to solve the same kind problem. Keywords: absorption coefficient multiple-layer absorption optimized design

Abstract: Ultrasonic surface rolling processing (USRP) is a surface nanocrystallization method developed recently, which can bring metal surface with superior properties. In order to obtain the motion state of the processing tip during USRP, a 3D dynamic finite element model was adopted to simulate the response of processing tip. The model parameters were provided by piezoelectric force sensor test system. Simulated results indicate that the peak value of impact force forms at the time of 25μ̓ and the maximum speed of working tip forms at the time of ̃̀μ̓.

Abstract: The graphite/CaF₂/TiC/Ni-base alloy composite coating was prepared on the surface of 45 carbon steel by plasma spray. Effects of loads, friction counterparts and lubricants on the tribological properties of the composite coating were investigated. The results show that the wear rate of the GCTN composite coating against Si₃N₄ is 0.67×10^-3mm³/m, which is about 2 times that against GCr15 steel, because Si₃N₄ induces micro-cutting wear of the composite coating. Water and NaCl solution may induce increasing of friction coefficients and wear rates. Especially, wear rate of the GCTN composite coating in NaCl solution is increased by 3.1 times compared with those under dry sliding and water. The GCTN composite coating presents better anti-wear property than Ni-base alloy coating in different environmental mediums.

Abstract: Firstly, surface deformation strengthening technology on steel was discussed, then, ultrasonic impact treatment (UIT), a newly-developed surface deformation strengthening technology, was elaborated. Finally, the surface of normalized LZ50 steel was treated by ultrasonic impact treatment (UIT) to verify the value of the technology. After UIT, a 130μm-thick hardened layer is produced and surface hardness is improved by 46%. Meanwhile, the compressive residual stress of the sample can reach 601Mpa and surface roughness is dramatically reduced to 0.21μm. All of the results are beneficial for the improvement of fatigue properties of steel.

Abstract: The process of explosive hardening of hadfield steel by a new flexible explosive was researched, and the change of hadfiled steel metallurgical structure was observed. The results show that: 1. Three times of explosive hardening by using 3mm explosive fill the demands of process (the surface hardness above 350HB,the hardening depth above 20mm,the sinkage below1.2mm and no crack in the surface);2. The hardness increment is decrease with explosive times increasing, and the hardness increment increase with the sinkage increasing;3.The internal hardness of the unprocessed hadfield steel is invariable basically, and the surface hardness is slightly fewer; the hardness of the hadfield steel hardening three times plunges largely when depth form 0mm to 2mm, and decreases gradually under 2mm.4.Grain refining, multiplication of dislocation and grain boundary sliding lead to the hardening of hadfield steel.