Papers by Author: Chang Sheng Liu

Abstract: In this paper, the intermediate layer was prepared by electroplating of nickel and WC particles. The parameters, including current density and temperature, were studied in the experiments. The measured methods, which consisted of surface roughometer and SEM, were used to character the roughness and microstructure. The experimental results showed that the optimizing parameters of the electroplating for composite texture were as follows, temperature was 65°C, current density was 5A/dm² and the pH value was 6.5. Under the condition of optimizing parameters the values of roughness Ra were in the range from 4.5 to 6.7 μm. From the microstructure observation by SEM revealed that the particles on the surface were well distributed. The difference of the electroplating time induced the different nickel contents which affected the binding force. The roughness of the surface was in the range of 1.35 to 4.47 μm.

Abstract: The generally textured techniques used in industry can make the roller surface fall off or damage by burning to form aculeate concave. The textured rollers produced by the method mentioned above have some disadvantage performances that include rapid roughness attenuation, limited use time and more concave. These disadvantages are not suitable for the formation of roughness on the cold roller surface. On account of high hardness and excellent wearable capability, the element chrome, which can be deposited on the cold roller surface, can increase the use life of textured cold roller enormously. In this paper, an experiment of DC superimposed pulse was performed to obtain certain roughness chrome textured and hemisphere-shaped chrome coatings. From the results, it was shown that the roughness and hardness of coating obtained by electroplating was 3.79μm at 850mA/cm2 and 1000 Hv respectively.

Abstract: A Ni-based alloy NiCrSiB laser cladding layer was made on the surface of CrNiMo stainless steel specimens using NiCrSiB powder. Cavitation erosion behavior of the laser cladding layer and the CrNiMo stainless steel was investigated by ultrasonic vibration cavitation erosion equipment The results shown that laser cladding layer has dense microstructure and has metallurgical combination with CrNiMo stainless steel substrate. Because of impact effect of cavities collapse, micro-cracks caused material broke off from samples. NiCrSiB laser cladding layer have better micro-crack propagate resistance property than CrNiMo stainless steel.Laser cladding layer has better cavitation resistance properties because of strengthening effect by precipitated phases such as M23[CB]6、CrB、CrSi、Fe2B、B4C and work hardening effect during cavitation erosion process.

Abstract: Two kinds of mixed powders:Ti-6Al-4V/B/C and Ti-6Al-4V/B4C which are pre-pasted on Ti-6Al-4V substrates separately were scanned by a 500W pulsed YAG laser to induce in situ formation of titanium composite coatings contained TiBx and TiC ceramic reinforced phases. The influences of laser processing parameters including Pulse Frequency (PF), Pulse Width (PW), Laser Power (P) and Scanning Speed (V) together with the powder proportions on the microstructure and properties of the coatings were investigated. Microstructure, phase components and micro-hardness of the coating were analyzed by OM, SEM, TEM, XRD and micro-hardness tester respectively. The optimized processing parameters of a single path laser scanned specimen in this case are as follows: PF: 15Hz, PW: 3ms, for the Ti-6Al-4V/B4C specimens the laser line energy ~12.5J/mm, for the Ti-6Al-4V/B/C specimens the laser line energy ~11J/mm. TiB and TiC ceramic were formed evenly reinforced in the matrix of Ti-6Al-4V with the morphology of needle, tiny dendrites and disperse spherical particles. The maximum micro-hardness of single-path layers is up to 750 Hv, which is over twice of that of the substrate (367Hv).The wear weight loss decreased nearly 3 times that of the substrate.

Abstract: The Al-Mg coatings were deposited on high-speed electro-galvanizing steel by using double-target DC magnetron sputtering. Numerous Al-Mg coatings were prepared with a range of different Mg-target power at different substrate temperatures. The morphologies and compositions were analyzed by SEM, EDS and XRD, the corrosion-resistance properties with different sputtering parameters were discussed by electrochemical measurement. It was found that with the substrate temperature increasing, the porosity decreased, meanwhile, higher substrate temperature resulted in more granular particles and an increased average particle size, but that did not affect corrosion properties obviously. The corrosion-resistance properties were found to be significantly affected by the targets power. As the power of Al-target and Mg-target were 900W and 200W respectively, the film acted the best corrosion-resistance property. Corrosion current density was approximately 4μA/cm2, decreased significantly compared with galvanized sheet. After analysis, the coating was mainly composed of Al12Mg17 which afforded sacrificial anode protection. As the Mg-target power over high relative to Al-target, the coating was composed of Al12Mg17 and MgZn2, the latter can cause micro-galvanic acceleration of corrosion.

Abstract: The laser surface alloying(LSA) technique was firstly used to form wear resistant layers on nodular cast iron rolls with two different powders, A: NiCr-Cr3C2 and B: C-B-W-Cr. The microstructure, element distribution and phases of the layers were investigated. Results indicate that the alloying layers had pores and cracks, as well as a metallurgical bonding with the substrates. For layers with powder A, as the thickness of the pre-layers decreased, the numbers of pores and cracks of the LSA layers decreased but the thicknesses of them were close. Phases were barely influenced by the thickness of the pre-layer, while the content of them were affected. For layers with powder B, as the laser specific energy increased, the numbers of pores and cracks in the LSA layers decreased and the thicknesses of them increased. The microstructure in the layers with different powders was different.

Abstract: Ti-51.45at.%Ni thin films were deposited onto copper substrates by magnetron sputtering. The copper substrates were pre-punched into dog-bone specimens with 4.5mm×30mm(gauge portion) ×35µm( thickness). The substrate temperature was about 673K. The thin films were about 20µm thick. The as-deposited films were first solution treated at 1073K for 1h, and then aged at 773K for 30min. The grain size was estimated to be 1.5µm from scanning electron microscopy micrographs. Tensile tests were carried out on CSS-44100 electron universal test-machine. The strain rate was 1.1×10-4 s-1. The stress-strain curves of the free-standing film were obtained from the experimental stress-strain curves of copper substrate together with the thin film adherent to the substrate compared with the curves of copper substrate without film. The Hall-Patch coefficient was calculated, k=205Mpa.µm1/2. It seems that the Hall-Patch coefficient decreases with increasing film thickness. The experimental results showed that a series of parallel cracks grew in a concerted fashion across the thin film and the cracks were equally spaced. The cracks were more closely spaced if the film stress was increased. The fracture toughness of the film was estimated, c KΙ =0.96MPa·m1/2. Therefore, the minimum crack spacing is predicted by the film stress given.