Study Of The Influence Of PVD And Nitriding On High Carbon High Chromium Cold Working Die Life

The lifetimes and properties of cold working die can hardly meet the demands of general market nowadays,so that it’s of great urgency to popularize the surface treatment on cold work die.Towards industrial population,this thesis reports the works in that two main plasma surface treatment techniques,which are plasma nitriding and arc ion plating,were applied on commonly used cold work die steel SKD11.Optical microscope,scanning electron microscope,X-ray diffraction,micro-hardness,Rockwell hardness as well as scratch test and tribological test were adopted for the characterization of the micro-structure and mechanical properties of nitrided layer and TiN and TiAlN coatings.The results are as follow.(1)Total thickness of nitrided layer is 141μm and 8μm of composite layer.Nitriding rate is about 8.41μm/h.Nitrided layer mainly compose of ε-Fe3 N,γ’-Fe4 N and CrN,and ε-Fe3 N is the main phase of composition layer.Surface roughness increases after nitriding.And the surface hardness of nitrided layer is 1158.5HV,resulting in a rise in wear-resistance of the sample.(2)The thickness of TiN and TiAlN coatings is 2.26μm and 2.17μm,respectively.They both form FCC B1 structure.TiAlN coating is a solid solution formed by the substitution of Ti atoms of Al atoms.Both coatings demonstrate strong(111)orientation.Microhardess of TiN and TiAlN coatings is 2644 HV and 3216 HV,respectively.The results of indentation tests show that the adhesion levels of TiN and TiAlN are HF3 and HF6 respectively,and HF1 of both PN+TiN and PN+TiAlN.However,scratch tests show that the adhesion forces of TiN and TiAlN are 30.8N and 11.8N respectively,while those of PN+TiN and PN+TiAlN are40.6N and 26 N respectively.The results of tribological tests indicate such relations on wear-resistance: PN+TiN>TiN,PN+TiAl N>TiAlN,TiN>TiAlN,in agreement with the results of adhesion tests.(3)According to the results of mechanical properties testings,nitriding and AIP TiN coating are chosen as surface treatment on SKD11 cold work punches to perform punch tests.The nitrided punches acquire an elongated lifetime in a low level while the TiN coated punches enjoy a lifetime three times longer than an untreated one.