This study examines the effects of ultrasonic nanocrystal surface modification (UNSM) on D2 cold-work tool steel materials. Specifically, the effect on surface topology and mechanical properties due to different UNSM conditions is examined. Before UNSM treatment, the substrate is processed via a quenching and tempering (QT) treatment for different values of substrate hardness. We observed surface changes due to UNSM treatments in D2 substrates and examined the correlation between topology changes, roughness, hardness, and tensile properties. The results indicated that hardness increased with the refinement of the substrate surface after UNSM treatment although significant changes based on the number or orientation corresponding to UNSM treatments did not occur. However, hardness increased significantly in non-QT substrates (which initially displayed relatively high elongation). Furthermore, in the substrates, surface roughness was degraded in specimens that underwent two passes of impacts compared with those that underwent a single pass. Conversely, in QT substrates, the double pass increased surface consolidation, and thereby improved surface roughness. Furthermore, tensile strength after UNSM treatment did not exhibit a significant difference irrespective of the number of treatments and orientations, or substrate hardness. However, in the non-QT substrates, variations occurred in the elongation based on the number of treatments and orientations. This can be owing to crack formation and surface roughness changes caused by material pile-up owing to ball tip impacts. Therefore, the UNSM conditions must be appropriately adjusted by considering the initial properties of the substrate before the treatment in conjunction with the properties that should be improved.

这项研究研究了超声纳米晶体表面改性（UNSM）对D2冷作工具钢材料的影响。具体来说，研究了由于不同的UNSM条件对表面拓扑和机械性能的影响。在进行UNSM处理之前，通过淬火和回火（QT）处理基板以得到不同的基板硬度值。我们观察到由于在D2基材上进行UNSM处理而导致的表面变化，并检查了拓扑变化，粗糙度，硬度和拉伸性能之间的相关性。结果表明，尽管未根据与UNSM处理相对应的数量或方向发生显着变化，但在进行UNSM处理后，硬度随基材表面的细化而增加。然而，非QT基材（最初显示出较高的伸长率）的硬度显着提高。此外，与经过单次冲击的试样相比，经过两次冲击的试样在基材中的表面粗糙度降低了。相反，在QT基板中，两次通过增加了表面固结，从而改善了表面粗糙度。此外，UNSM处理后的抗张强度没有显着差异，与处理的次数和方向或基材硬度无关。然而，在非QT基板中，基于处理次数和取向，伸长率发生变化。这可能归因于由于球头撞击而造成的材料堆积导致的裂纹形成和表面粗糙度变化。所以，