Friction And Wear Characteristic Of Laser Quenched Ferrous P/M Materials

Ferrous powder metallurgical materials possess enormous potential marketand have been developed rapidly. Recently, the more and more ferrous P/Mmaterials instead of a part of wrought steels and casting irons are used tomanufacture high performance structure components, such as automotive gears,camshafts and connecting rods which would be difficult and expensive to make bymachining. However, P/M materials'tribological and mechanical properties arelimited by the residual porosity. In this paper, we apply the laser quenching to thesamples. As a result, the surface with high intensity and good wear resistance isobtained. The application field of powder sinter technology is widened andproperties are improved.In this study, high performance P/M steel samples alloyed mainly with Ni,Cr,Cu,Mo and C are prepared in single press and single sinter technique and are laserquenched. The structures and properties of sintered and quenched ferrous P/Msamples are researched by means of optical microscopy , scan electron microscopy(SEM), microhardness instruments and X -ray analysis. The tribologicalcharacteristics of samples have been studied by using MG-2000 tribotester. Thesurface appearance and composition of wear track are examined by means of SEM.The main purpose of this study is that the laser quenching technique is used toimprove the properties and tribological characteristics of materials and theinfluence of ferrous P/M materials'content of Cr are discussed. The specific workis as follows:(1) Alloy designing and preparation of ferrous P/M materials.Alloy elements can improve P/M materials. The most common alloys are C,Cu,Ni,Mo and Cr . According to the functions of the elements, their contents areas follows: Ni:2%, Cr:0.5%,1.0%,1.5%,2.0%,2.5% Mo:0.85%, C:0.5%, Cu: 2.0%.The samples are pressed, sintered and laser quenched. The research shows that thebest output is 3.2kw,scan speed is 8mm/s. (2) The structures and properties investigation of laser quenched samples. The metallographic structures of sintered ferrous P/M materials are ferrite andpearlite. From the surface to the center, the quenched samples'microstructures areas follows: the first layer is hardened layer. It is made up of fine martensite andretained austenite. Its thickness is 1.0～1.2mm. The second layer is the transitionlayer. Its microstructures are martensite,ferrite and cememtite. The third layer ismatrix. It consists of ferrite and pearlite. The quenched samples'microhardness is HV0.3623～669 3 times higherthan the sintered samples'. (3) The research about tribological characteristics of ferrous P/M materials. Ferrous P/M materials'wear resistance has been improved after they are laserquenched. Wear quantities and friction coefficients are descendant. In the range ofexperimental loads, sintered samples'wear quantities increase with theincreasement of the load. So do the quenched samples'wear quantities. The frictioncoefficients decrease with the increasement of the load. In our research, thesamples'sliding speeds are 0.785m/s and 1.256m/s. The wear quantities of theformer are fewer than those of the latter, but the friction coefficients are larger thanthose of the latter. During the wear of sintered P/M materials, adhesion wear,abrasive wear anddelamination wear happen. The dominant mechanism is adhesion wear. After P/Mmaterials are laser quenched, their dominant mechanism is oxidation wear. Whenload is low(40N-80N), oxidation film's formation is slower than its destroy. Thenthe main mechanism is oxidation wear and abrasive wear. When No.1 is at the 80N...