Effects And Mechanism Of Alloy Elements On The Compression Properties Of TiC_xN_y-TiB₂/Ni Composites

TiB₂and TiC_xN_yceramics have been advisable candidates for the electrodes andcuttingtools due to an excellent combination of superior mechanical （such as high hardnessand high modulus） and physical properties （like low density, high electrical conductivity andhigh melting point） as well as good abrasive resistance. Besides, it is believed that comparedwith the monolithic ceramics would exhibit enhaced compressive performance and higerwear resistance. Meanwhile, the metal Ni has the good ductility, impact resistance,temperature resistance and corression resistance. And Ni has good wettability with TiB₂andTiC_xN_yceramics. Combustion Synthesis has many advantages, such as the uniformlydispersing ceramic, clean particle–matrix interface and the simple and low–cost preparationtechnique. However, a large number of cavities existed in the products fabricated bycombustion synthesis leads to poor properties of the composites. In order to improve therelative density of the products, an additional mechanical pressure was applied, and theapproach is commonly defined as combustion synthesis and hot press consolidation. In thisstudy, effects and mechanism of alloy elements on the compression properties ofTiC_xN_y–TiB₂/Ni composites are investigated.In this paper, the （TiC_xN_y–TiB₂）/（Ni+W） composites were fabricated successfully bythe method of combustion synthesis and hot press consolidation in the Ni–W–Ti–B4C–BNsystem. The effect of the content of alloy elements （W, Cr, Mo, Co, Al, V） on themicrostructure, compression properties and abrasive wear behavior of the composites wasinvestigated. The results are listed as followed:（1） The compact nickel matrix composites reinforced by TiC_xN_y–TiB₂biphase ceramicswere successfully fabricated by the method of combustion synthesis and hot pressconsolidation in the Ni–Ti–B4C–BN system. With the increase in the Ni content, themaximum combustion temperature decreases, and the mean sizes of TiC_xN_yand TiB₂inthe composites with30wt.%,40wt.%,50wt.%and60wt.%are5μm,2μm,>1μm and <1μm, respectively; and the relative densities are94.8%,97.3%,97.6%and96.7%, respectively.（2） With the increase in the content of TiC_xN_y–TiB₂, the microhardness increases from1014HV to1560HV, and the abrasive resistance increases by two times under theapplied load of35N and the Al₂O₃abrasive particle size of106μm. With the size ofTiC_xN_y–TiB₂decreases from70wt.%to50wt.%, the compression strength increasesfrom2.94GPa to3.3GPa. That’s because of defining ceramic particles and increasingrelative denstity. The relative density plays a significant role in compression strength.With decreasing Ni content to40wt.%, the compression strength decreases to2.8GPasince the size of ceramic particles and the relative density of composites remainunchanged while the content of ceramic particles decreases. In this paper, the samplewith50wt.%Ni possesses the maximum compression strength.（3） The effects and mechanism of alloy elements on the constituents and mirostructures ofTiC_xN_y–TiB₂/Ni composites. With increase of W, Cr, Mo, Cr from0wt.%to8wt.%, thesizes of ceramic particles decrease from5μm to2μm,800nm,900nm,3μm, respectivelyand the relative densities of the composites increase. The ceramic particles don’t changegreatly while the porosity increases due to released heat by the exothermic reations of Alwith Ni or Ti.（4） The effects and mechanism of alloy elements on the microhardness, compressionproperties and abrasive resistance of TiC_xN_y–TiB₂/Ni composites are revealed.With the increasing W, Cr, Mo, Al, Co, V content from2to5wt.%, thecomprehensive properties of the composites increase. W and Cr can improve thecomprehensive properties effectively.（a） The composite with5wt.%W processes the best comprehensive properties in thispaper: the hardness （2018HV）, the compression strength （4065MPa）, the fracturestrain （4.2%）, resulting in an overall increase by457HV,1125MPa and1.31%,compared with these of the composite without the addition of W, respectively; theabrasive wear resistance of the composite with5wt.%W is1.6times as high as thecomposite without the addition of W under the applied load of35N and the Al₂O₃abrasive particle size of20μm.（b） The composite with5wt.%Cr processes the relative good comprehensive properties:the hardness （1824HV）, the compression strength （3.65GPa）, the fracture strain（3.4%）, resulting in an overall increase by263HV,0.71MPa and3.4%, comparedwith these of the composite without the addition of Cr.（5） In conclusion, the strengthening effects of the alloying elements are in order ofW>Cr>Al>Mo>Co>V. The mechanism of alloy elements on the compression properties can be summarized as followed: the refinement of ceramics, the increasing relativedensity and the formation of reinforced phase.