Technology And Performance Of Ni-based Coating Fabricated By Mechanical Alloying

Metal powder are strongly squeezedor crashed by hard milling balls while themechanical-alloying happened inside the milling can and the crash-induced heat couldweld the metal powder to the can surface. Also the long-time squeezing and weldingreaction will generate a relative condensed coating layer. According to thismethodology, milling time, milling speed and powder categoryare discussed toillustrate the coating-form mechanism and the effects of the three elements arerespectively demonstrated as well.The chemical compositions and phases of Ni-Al based coating are analyzed viaX-Ray diffraction(XRD), Scanning electron microscope (SEM) and energy dispersiveX-ray spectroscopy (EDS) while the mechanical properties are assessed bymicro-hardness tests, thermal shock tests, high-temperature oxidation resistance tests,corrosion resistance tests and tribological experiments. Based on the mentionedexperimental methodology above, the main results are obtained as follows:Firstly, Ni and Al powder were mixed at a mass ratio of4:1and then the mixturewere grinded at speeds of200rad/min,400rad/min and600rad/min respectively.After the milling, conclusion that the coating thickness changed with milling speedsand a well-structured consensus layer which was surprisingly as thick as130um wasobtained at the speed of400rad/min were found. To further understand the coatingmechanism, Ni powder, Ni-0.1Al-0.1Cr powder, Ni-0.2Cr powder and Ni-0.2Alpowder at the milling speed of400rad/min were invested, and the conclusion was theseries Ni-0.2Al powder coating formed the most condensed and continuous. Thereforethe speed of400rad/min was closed with the Ni-Al powder system and effects ofballs/powder ratio(5:1and10:1, respectively) was discussed and the balls/powderratio of5:1could better coating construction in terms of consensuses.Also, Ni-Al based coating system was invested after according experimentalmethods with different Al-containing percentage of0.2,0.4,0.6, and0.8and withgrinding time of6h,12h,18h, and24at grinding of400rad/min. As results ofhardness tests, the hardness of coated layer showed an increasing tendency while themilling time prolonged. Additionally, the hardness of Ni-Al coating layers decreasedwhile the Al-containing percentage improved but the high percentage of Al mayenhance the corrosion resistance. Furthermore, the coating spelling resistance firstincrease then decrease in the Ni-Al system of powder with increasing milling time via thermal shock experimental results. High temperature oxidation test shows that longermilling time can reduce the high temperature oxidation resistance,After all, milling time, powder category and milling speed are invested anddiscussed to demonstrate the coating forming mechanism.