High Temperature Wear Properties Of The TiC_x,TiC_x-TiB₂ Particulate Reinforced Steel Matrix Composites

Wear is one of the three practical failure forms in steel materials, and annual economical lost caused by wear failure is quite large, according to figures released by U.S., economic lost due to wear failure was high as much as 100 billion dollars annually. In the former Soviet Union, economical lost caused by wear was also quit large. While China was still a lack of comprehensive statistics, because our wear-resistant properties of workpieces is poorer compearing with the developed countries', wear life of many basic parts in China are generally lower than the level of foreign advanced products, which had became a heavy economic burden. In different working conditions, wear failure of material is different, some are overall failure, while others partial failure, such as the excavator shovel teeth, seamless steel tube head, hammer crusher and so on, and composite materials will be the best way to resolve this problem. Working areas own good high wear resistance, while the non-wear parts own high toughness, metal matrix composite materials will have a very good application prospect.In recent years, in-situ method as a simple preparation process, which is due to low cost, good interface between reinforcement and substrate, has been widely applied to the preparation of particle reinforced metal matrix composites. Because composites prepared by this method have bad density, we have adopted a Vacuum-casting technology to resolve these problems successfully. This method owns the following several advantages: 1. Particle volume content can vary from 60Vol.% to 90 Vol.%. Material density is reduced, whose wear resistance is improved at the same time, and working life can be improved greatly; 2. Large, complex shape of the particle reinforced steel matrix composites working pieces can be cast; 3. Process is relatively simple, which is easy to promote large-scale production.In our work, the high volume fraction of TiC_x or TiC_x-TiB₂ particulates locally reinforced die steel matrix composites were successfully fabricated using the combustion synthesis during the casting process deried from Ni-Ti-C and Ni-Ti-B₄C respectively. We have studied influence of TiC_x-TiB₂ and TiC_x volume content in locally reinforced region, temperature and load on microstructure and high temperature wear properties, and we discussed the abrasive wear mechanism and oxidation wear mechanism of composite. Meanwhile we also study enfluence of particle content in the locally reinforced region on its oxidation resistance, and optimize the best particle volume content. We also explored its high-temperature oxidation mechanism.The main results of this study are as follows:(1) We made use of combustion synthesis combined with V-cast method to fabricate TiC_x and TiC_x-TiB₂ reinforced die steel matrix composites, the microstructure clearly divided into three parts: local enhanced zone, transitional zone and die steel matri. The interface between enhance district and the substrate is good. The reaction products was relatively pure, which mainly includs TiC_x, TiB₂ reinforcements, [Fe, Ni] solid solution and ?-Fe. When designed content of TiC_x-TiB₂ and TiC_x in partical locally reinforced region was 60Vol.%, the sizes of partical were most fine, whose size were ¹?m and 1³?m respectively.(2) The density experiment showed that density of partical locally reinforced reingion increased with designed partical content increasing. This was mainly due to that the designed partical content in the locally reinforced region was high, the combustion temperature was high, gas could gain greater expansion, liquid steel can get more infiltration into local reforced region. This resulted in increasing density of locally reinforced region with designed partical content increasing.(3) We proposed influence law of ceramic's type in locally reinforced region on its law of high temperature oxidation behavior from high to low: TiC_x -TiB₂> TiC_x> die steel matrix; at the condition of 600℃in air, the composite with 60Vol.% of TiC_x-TiB₂ and TiC_x performed best high-temperature oxidation property. This was mainly due to smaller particle size of composite was beneficial to the formation of the oxide film with small size, uniform thickness.(4) We found influence law of ceramic's content in locally reinforced region on its high temperature oxidation behavior of law from high to low: TiC_x-TiB₂> TiC_x> die steel matrix; in our experimental conditions, the composite with 60Vol.% of TiC_x-TiB₂ and TiC_x respectively performed best high-temperature wear property, whose high-temperature wear property was increased by 9 times than die steel matrix.(5) We revealed the temperature's influence on wear mechanism of TiC_x and TiC_x-TiB₂ reinforced composites: With the increase of experimental temperature (room temperature⁷00℃), the wear mechanism varied as fllows: adhesive wear + abrasive wear→wear abrasive wear and oxidation→wear oxidation.(6) We found the best systems and optimal process parameters of TiC_x or TiC_x-TiB₂ locally reinforced hot work die steel composite: Ni-Ti-B₄C system, when design Ti:B₄C was 3:1, composites behaved best; the designed TiC_x-TiB₂ particle content in the locally reforced region: 60Vol.%.