Study On The Mechanical Properties Of (Ti,V)C/Fe Produced By In-situ Synthesis

Wear, corrosion and fracture are primary forms of materials failure. The main reason of materials failure is wear caused friction. About 70%～80% equipment damage is resulted from various wear. Investigation results that done by Britain and USA indicate that the expense brought material failure is estimated about one hundred billion $ in one year; economic benefit brought by improving lubrication and decreasing wear accounts for over 2% of Gross National Product. In addition, with high-speed development of modern industry, it is urgent that some parts, (for example, camshaft and jib of engine, guided wheel and roller of rolling mill et al.)should be used under some conditions such as high-temperature, high-speed and wear-resistance. Meeting these needs is becoming difficult for present iron and its alloy, therefore, it is very important in economy and application to develop new wear-resistance materials and systematically investigate their friction and wear.Because steel matrix composites have the merits such as high (specific strength)compare intensity, compare modulus, wear-resistance, new materials focus on particulates reinforced iron matrix composites. As far as particulates reinforced iron matrix composites are concerned, most of the work on iron-based composites has involved TiC reinforcement, which is introduced in the iron matrix through a powder metallurgy (P/M) route and in-situ synthesis route. Among the in-situ synthesis techniques, self-propagation high-temperature synthesis(SHS) and casting technologies are widely used to produce Fe-TiC composites. If combining in situ with powder metallurgy technique to produce particulates reinforced iron matrix composites, the problems of cast defects lying in casting and densification in SHS will be solved, and the difficulty of the weak interface bond between the matrix and the reinforcement in powder metallurgy will be overcome.Panzhihua-Xichang area in Sichuan is abundant in vanadic titianomagnetite deposit. Because vanadium and titanium are transition metals and the difference between their atomic numbers is only 1, titanium carbide (TiC) and vanadium carbide (VC) are refractory, high hardness and thermodynamically stable metal carbides. Moreover, the wettability between VC and Fe is good, so VC is also a perfect reinforcement in iron matrix composites. However, there have been few studies on VC particulate reinforced iron matrix composites, even no study has ever tried to fabricate (Ti,V)C particulate reinforced iron-based composites. Therefore, the research of (Ti,V)C particulate reinforced iron-based composites has its own novelties and important scientific value.In this paper, a novel process which combines in situ with powder metallurgy technique, was used to produce (Ti,V)C particulates reinforced iron matrix composites. The kinetics of Fe-Ti-V-C system, sintering densification, microstructure and mechanical properties of (Ti,V)C particulates reinforced iron matrix composites were lucubrated systematically by means of various analytical techniques such as SEM, XRD, DTA.The reaction kinetics of Fe-Ti-V-C system was studied by DTA and XRD. Results showes that first, allotropic change Fe_α→Fe_γand FeV+C→VC+Fe at 765.6℃; second, formation of the compound Fe₂Ti at 1058.5℃because of. the eutectic reaction between Ti and Fe; third, reaction between carbon and melted Fe₂Ti causing formation of TiC at 1140.4℃; finally, (Ti,V)C formation as increasing temperature.The investigation for sintering densification of (Ti,V)C/Fe matrix composites indicates the best sintering temperature was 1420℃for composites whose V/Ti atomic ratio was from 0 to 0.2 while it was 1400℃when V/Ti atomic ratio varied from 0.4 to 1.0. At optimal sintering temperature, a densification above 98% was obtained in all compositions.The microstructure of (Ti,V)C/Fe matrix composites was analyzed with the help of XRD, SEM, TEM. Results showed (Ti,V)C reinforcement was synthesized in-situ, and Fine (Ti,V)C particles generated in situ were uniformly dispersed in the pearlite matrix. Additionally, with the increasing of V/Ti atomic ratio, on one hand, morphology of (Ti,V)C particles transformed from irregular to spherical; on the other hand, (Ti,V)C particles evidently minishing at first and then growth were observed.The research on mechanical properties of (Ti,V)C/Fe matrix composites indicated the bending strength of the (Ti,V)C/Fe matrix composites increased at first and then decreased with the increase of V/Ti atomic ratio, reaching maximum at V/Ti atomic ratio being 0.2. As for composites (V/Ti atomic ratio being 0,0.1,0.2) containing approximately the same volume fraction., the bending strength raised with the average grain size of carbide decreasing. Compared to the sample(V/Ti atomic ratio being 0),the grain sizes of (Ti,V)C reinforcement of the composites(V/Ti atomic ratio being 0. 1and 0. 2) got smaller apparently and the bending strength became higher. At the same time, bending strength of the sample (V/Ti atomic ratio being 0. 2) was not only higher than the sample (V/Ti atomic ratio being 0) ,but also higher than the one whose V/Ti atomic ratio was 0. 1. Because of the addition of vanadium increasing, morphology of (Ti,V)C particles got rounder and the spherical (Ti,V)C reinforcement uniformly dispersing in Fe matrix can avoid stress concentration or plastic deformation. As for composites (V/Ti atomic ratio being 0. 4,0. 6,0. 8,1. 0),with the increase of V/Ti atomic ratio, on one hand, the volume fraction of (Ti,V)C decreased, on the other hand, the average grain sizes of (Ti,V)C increased. That is the reason why bending strength got down gradually.The relative wear-resistance of the (Ti,V)C/Fe matrix composites subjected to quenching and low-temperature temper treatment was from is 1.4 times to 3.29 times than high chromium white iron subjected to sub-critical treatment. Through analyzing the surface topography, it was known that the dominant wear mechanism of the (Ti,V)C/Fe matrix composites under abrasive wear condition was microcracking and microploughing. Loss of the composite happened in the process of relative motion between the composite and the abraser. As for this kind of material, wear-resistance was improved through stopping the abraser puncturing into the martensite and further ploughing. At the meantime, V/Ti atomic ratio represented great influence on the wear-resistance. When it was zero, the grain size of TiC was relatively bigger and the particles spacing interval was longer, so that was easy for the abraser to puncture into martensite matrix and plough for a long distance, leaving many wide and deep grooves on wear surface.Compared to the composites (V/Ti atomic ratio being 0), the grain sizes of (Ti,V)C reinforcement of the composites(V/Ti atomic ratio being 0. 1and 0. 2) got smaller apparently and the particles spacing interval became shorter. Hence, it was hard for the abraser to puncture into martensite matrix. The wear surface appeared smooth and the ploughing grooves were narrow and shallow. The wear-resistance represented well. With the addition of vanadium increasing, on one hand, the volume fraction of (Ti,V)C decreased, on the other hand, the average grain sizes of (Ti,V)C increased, both of them caused the particles spacing interval being longer. So the effect of stopping abraser from ploughing by (Ti,V)C reinforcement was weaken, abrasive wear aggravated and wear-resistance got falling down gradually. In short, wear-resistance of the composites achieved the best at V/Ti atomic ratio being 0.2...