Wear Properties Of Gray Cast Iron Processed By Laser Bionic Coupling Technique After Thermal Fatigue

Some important parts work in harsh conditions. Their life is limited by multiple factors. For example, the main failure forms of brake drums and hot work rolls are wear and thermal fatigue. In a fatal accident which caused by a fragment of broken gray iron brake drum, the detach of fragment part from drum is the result of friction form wear and crack from thermal fatigue. Therefore, it’s very urgent to make a improvement on the service life of parts, which work under the multiple conditions of wear and fatigue. Most traditional research focus on a single performance by improve from one single factor. It can not solve the problem caused by multiple factors. And this also makes the gap between laboratory test results and the actual conditions larger. Due to the current experimental conditions, it is impossible to apply both wear and thermal fatigue tests simultaneously on a same sample at the same time. In the real working conditions of brake drum and rolls, the working process is the cycling of thermal fatigueâ†'wearâ†'thermal fatigue. So the research can get close to real conditions by study the wear performance after thermal fatigue. According to previous studies, bionic coupling processing can improve the thermal fatigue and wear resistance respectively. And this performance improvement is significantly. According to bionics coupling theory, bio-surface evolved through thousands of years to maximize their ability of adaption to a variety of harsh environments. So bionic coupling process is potential in the research of multi-factor performance enhancement.Based on the bionic coupling theory, this paper researched a bionic laser processing by imitating the shell which survive in similar environments. The shell surface is a construction of multiple coupling characteristics. A variety of coupling structure were processed by laser melting and cladding. The characteristics changes after thermal fatigue were observed. The wear properties and the mechanism before and after fatigue were analyzed. The suitable strengthen method and related parameters were presented. The main conclusions can be concluded as follows:1. This study found that thermal fatigue increased wear loss of specimens. The wear weight loss of each specimen grow with increasing thermal fatigue cycles. The mass loss of untreated gray iron specimen increased a lot with thermal fatigue cycles. It raises in a form of exponential. Bionic coupling processing can significantly improve the wear resistance after thermal fatigue. Bionic laser remelting processing enhanced the wear resistance before and after thermal fatigue. And mass loss were increased in a form of linear. The wear resistance of bionic specimen drops slower than that of untreated one.2. This study also found that higher temperatures accelerated the wear resistance drop after thermal fatigue. The mass loss of untreated gray iron specimen after700℃thermal fatigue is1.8times higher than that after500℃thermal fatigue. Bionic laser remelting process enhanced specimen wear resistance at every thermal fatigue on different temperature. And the wear resistance dropped slower with temperature. The mass loss after700℃thermal fatigue is1.3times of that after500℃thermal fatigue.3. Different bionic units on performance can be processed by laser cladding different powder. By laser cladding mixed WC or Cr powder, hard phases of carbide or solid solute with Cr can be processed. The units with enhanced form of carbide includes carbide particles harden or carbide precipitation harden. The performance of the units with the harden form of carbide particles decreases rapidly with thermal fatigue cycles. Its wear resistance after fatigue is even lower than that of laser remelting unit. The wear resistance of carbide precipitation unit is the best of all others before thermal fatigue. It dropped moderate with thermal fatigue cycles. So it’s better than laser remelting unit after thermal fatigue. The enhance amplitude of Cr solid solution unit is not obvious than that of carbide precipitation unit before thermal fatigue. But its wear resistance dropped slower with thermal fatigue.4. The thermal cracks can be suppressed by adjusting the shape, alignment angle and arrangement interval of bionic units. It reduced the cracked area and the mass loss of bionic processed specimen after thermal fatigue. The studies have proved that the wear resistance can be enhanced by the unit arrangement of closely spaced and perpendicular to the direction of crack on2-dimensional plane.5. There are three phenomenon found on the gray cast iron after thermal fatigue: surface cracking, hardness reduction and oxidation. These combined three factors reduce the wear resistance of untreated gray iron specimen after fatigue. Bionic laser remelting unit can reduced cracking area on specimen, improve the hardness after thermal fatigue and restrict surface oxidation. By adjusting coupling factor of material can improve the microhardness before and after thermal fatigue further. By adjust the bionic factors of shape and characteristics can limit the cracks on untreated areas in a further degree. The adjustments on two coupling factors above will improve the wear properties of the bionic specimen after thermal fatigue further.