Study Of Tribological Properties Of Cr-base Hard Films Deposited On Clinching Tools

As a joining technology of efficiency, high tensile, strong applicability, and energyconservation, clinching has been widely used in lightweight industry for metal sheetconnection. As a type of cold extruding tools, clinching tools must work in the severeconditions. Nowadays, the automobile, aerospace and electronics industries are developingtowards high efficiency and energy-saving, as well as good quality and large quantity. Suchtrends result in increased frequency of wear and tear, and plastic abrasion, deformation,cracking are the primary failure modes of clinching tools. In this thesis, the applicationobjects is clinching tool, and PVD is applied to deposit a Cr-base hard coating on the steelsurface of DC53cold extruding tool. This thesis is also going to evaluate the tribologicalproperties of the Cr-base hard coating through experiment and simulation.With the technology of closed field unbalanced magnetron sputter ion pla ting (CFUMSIP),CrN CrAlN and CrTiAlN hard coatings were deposited on the surface of DC53steel andSi(100). The microhardness and adhesion of the coatings were evaluated by microhardnesstester and Rockwell apparatus respectively.Sliding wear tests of the CFUMSIP CrN, CrAlNand CrTiAlN coatings against WC-Co alloy balls and GCr15bearing steel balls has beencarried out on a POD high temperature tribometer under ball-on-disc (unidirectional) slidingconditions. Optical microscope, X-ray diffractometer (XRD), field emission scanning electronmicroscopy (FESEM) and energy dispersive spectrometer (EDS), were used to study thetribological properties of Cr-base hard coatings. The results are as follows:(1) The technological parameters, such as bias voltage, OEM value and Cr-target currenthave a great effect on the microhardness and adhesion of Cr-base hard coatings. And thecoatings deposited by CFUMSIP system mainly grew with (111) preferred orientation, andpresent a columnar structure with good mechanical properties.(2) In the room temperature friction-wear tests, the CrN, CrAlN and CrTiAlN specimensshowed wear rates as1/18,1/16,1/23times as the DC53steel respectively. In hightemperature friction-wear test, as the result of rapid oxidation of Al, the Al2O3layer coveredon the surface enhanced the coating’s abrasive resistance obviously. And because of the high microhardness of TiN, CrTiAlN had the best abrasive resistance, and CrAlN took the secondplace. The wear forms of Cr-base hard coatings were shown as adhesive wear and oxidativewear in both of the room temperature and high temperature tests.(3) For all of the three Cr-base coatings, as the result of lower microhardness of GCr15, thefriction pair produce more abrasive dust in the tests rubbed with GCr15ball than in the testsrubbed with WC-Co ball, which aggravated the adhesive wear and resulted in abrasive wear.In the lubricated friction-wear test, the wear rate of Cr-base coatings were reduced substantiallyby the lubricating oil with e.p. additive, and as a result of chemical reaction between coatingsand oil, the friction showed light adhesive wear and corrosive wear.