Researcher, National Centre of Rapid Prototyping, Technical University of Cluj-Napoca, Cluj-Napoca, Romania.
Researcher professor and Head of Polymeric Composite Laboratory, Institute for Research in Chemistry Raluca Ripan, Babes-Bolyai University, Cluj-Napoca, Romania.
J Prosthet Dent. 2022 Sep;128(3):421-429. doi: 10.1016/j.prosdent.2020.11.043. Epub 2021 Feb 18.
The selective laser melting (SLM) process has become popular for the fabrication of frameworks for metal-ceramic restorations, although their surface roughness is greater than with cast or milled frameworks. Limited information is available regarding the surface mechanical characteristics of cobalt-chromium (Co-Cr) SLM-manufactured restorations.
The purpose of this in vitro study was to adapt the laser parameters for a remelting strategy, scanning the outer boundary of Co-Cr specimens, to reduce surface roughness and solidification defects, to determine microhardness, to investigate surface morphology and microstructure, and to establish surface mechanical characteristics.
Co-Cr specimens were SLM manufactured by using a typical melting (TM) strategy and an adaptive remelting (AR) strategy. The AR strategy involves rescanning 50% of the contour, varying the laser parameters. The roughness parameters considered were Ra and Rz. Vickers hardness was measured by microindentation with a 9.81-N force (ASTM E384-17). The surface morphology was investigated by scanning electron microscopy, the chemical composition by energy-dispersive X-ray spectroscopy, and the phase identification by using X-ray diffraction. The mechanical surface properties measured were the nanohardness, elastic modulus, and dissipation energy. One-way ANOVA with the Tukey procedure was used to compare the groups (α=.05).
The innovative AR strategy reduced the surface roughness by 45% compared with TM, comparable with their cast counterpart. The smoothest AR surface was obtained by using 75 W and 350 mm/s for the first scanning of the contour, followed by a second remelting with 80 W and 700 mm/s. The microstructure of AR specimens had limited solidification defects, a chemical composition similar to that of raw powder, and a surface microhardness over 600 HV1. A fine grain structure in a single matrix phase was detected both on TM and AR specimens. The mechanical characteristics of the smoothest Co-Cr surface were 218 GPa elastic modulus, 746 HV Vickers nanohardness, 21 243 pJ plastic energy, and 26% nanoindentation work ratio. Significant differences were observed between the melting strategies (P<.05) both for surface roughness and microhardness.
The laser scanning strategy affects both the surface roughness and the hardness of SLM-manufactured specimens. The results show that using the AR strategy and proper laser parameters can reduce the roughness and increase the surface hardness of Co-Cr specimens made of conventional powder feedstock.
选择性激光熔化（SLM）工艺已广泛用于制造金属陶瓷修复体的框架，尽管其表面粗糙度大于铸造或铣削框架。关于 SLM 制造的钴铬（Co-Cr）修复体的表面力学特性，目前仅有有限的信息。
本体外研究的目的是调整激光参数以采用重熔策略，扫描 Co-Cr 试样的外边界，以减少表面粗糙度和凝固缺陷，确定显微硬度，研究表面形貌和微观结构，并建立表面力学特性。
使用典型的熔化（TM）策略和自适应重熔（AR）策略，通过 SLM 制造 Co-Cr 试样。AR 策略涉及以 50%的轮廓重新扫描，改变激光参数。考虑的粗糙度参数为 Ra 和 Rz。用 9.81-N 力（ASTM E384-17）进行维氏硬度微压痕测量。用扫描电子显微镜研究表面形貌，用能量色散 X 射线光谱法研究化学成分，用 X 射线衍射法进行物相鉴定。测量的机械表面性能为纳米硬度、弹性模量和耗散能。采用单因素方差分析和 Tukey 检验进行组间比较（α=.05）。
与 TM 相比，创新的 AR 策略将表面粗糙度降低了 45%，与铸造的 Co-Cr 修复体相当。采用轮廓第一次扫描时 75 W 和 350 mm/s、第二次重熔时 80 W 和 700 mm/s 的参数，获得了最光滑的 AR 表面。AR 试样的微观结构凝固缺陷有限，化学成分与原始粉末相似，表面显微硬度超过 600 HV1。在 TM 和 AR 试样中均检测到单一基体相中细小的晶粒结构。最光滑 Co-Cr 表面的机械特性为 218 GPa 弹性模量、746 HV 维氏纳米硬度、21 243 pJ 塑性能量和 26%纳米压痕功比。两种熔化策略（P<.05）在表面粗糙度和显微硬度方面均有显著差异。
激光扫描策略会影响 SLM 制造的试样的表面粗糙度和硬度。结果表明，采用 AR 策略和适当的激光参数可以降低 Co-Cr 常规粉末进料试样的粗糙度并提高其表面硬度。
