Lim Tae-Hwan, Lee Chang-Soon, Cho In-Sik, Amanov Auezhan
Department of Advanced Materials Science, Sun Moon University, Asan 31460, Korea.
Department of Mechanical Engineering, Sun Moon University, Asan 31460, Korea.
Materials (Basel). 2020 Jul 16;13(14):3172. doi: 10.3390/ma13143172.
The current research reports the improvement in surface integrity and tribological characteristics of steel prepared using a powder metallurgy (PM) by ultrasonic nanocrystal surface modification (UNSM) at 25 and 300 °C. The surface integrity and tribological properties of three samples, namely, as-PM, UNSM-25 and UNSM-300 were investigated. The average surface roughness of the as-PM, UNSM-25 and UNSM-300 samples was measured using a non-contact 3D scanner, where it was found to be 3.21, 1.14 and 0.74 µm, respectively. The top surface hardness was also measured in order to investigate the influence of UNSM treatment temperature on the hardness. The results revealed that the as-PM sample with a hardness of 109 HV was increased up to 165 and 237 HV, corresponding to a 32.1% and 57.2% after both the UNSM treatment at 25 and 300 °C, respectively. XRD analysis was also performed to confirm if any changes in chemistry and crystal size were took place after the UNSM treatment at 25 and 300 °C. In addition, dry tribological properties of the samples were investigated. The friction coefficient of the as-PM sample was 0.284, which was reduced up to 0.225 and 0.068 after UNSM treatment at 25 and 300 °C, respectively. The wear resistance was also enhanced by 33.2 and 52.9% after UNSM treatment at both 25 and 300 °C. Improvements in surface roughness, hardness and tribological properties was attributed to the elimination of big and deep porosities after UNSM treatment. Wear track of the samples and wear scar of the counter surface balls were investigated by SEM to reach a comprehensive discussion on wear mechanisms. Overall, it was confirmed that UNSM treatment at 25 and 300 °C had a beneficial effect on the surface integrity and tribological characteristics of sintered steel by the PM that is used in a shock absorber for a car engine.
当前研究报告了通过在25℃和300℃下进行超声纳米晶表面改性（UNSM）制备的粉末冶金（PM）钢的表面完整性和摩擦学特性的改善情况。研究了三个样品，即PM态、UNSM-25和UNSM-300的表面完整性和摩擦学性能。使用非接触式3D扫描仪测量了PM态、UNSM-25和UNSM-300样品的平均表面粗糙度，发现分别为3.21、1.14和0.74μm。还测量了顶面硬度，以研究UNSM处理温度对硬度的影响。结果表明，硬度为109 HV的PM态样品在25℃和300℃进行UNSM处理后，硬度分别提高到165 HV和237 HV，相应提高了32.1%和57.2%。还进行了XRD分析，以确认在25℃和300℃进行UNSM处理后化学性质和晶体尺寸是否发生任何变化。此外，还研究了样品的干摩擦学性能。PM态样品的摩擦系数为0.284，在25℃和300℃进行UNSM处理后分别降低到0.225和0.068。在25℃和300℃进行UNSM处理后，耐磨性也分别提高了33.2%和52.9%。表面粗糙度、硬度和摩擦学性能的改善归因于UNSM处理后大而深的孔隙的消除。通过扫描电子显微镜（SEM）研究了样品的磨损轨迹和配对表面球的磨损疤痕，以全面讨论磨损机制。总体而言，证实了在25℃和300℃进行UNSM处理对用于汽车发动机减震器的粉末冶金烧结钢的表面完整性和摩擦学特性具有有益影响。
