• The Journal of Advanced Prosthodontics
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• 제9권1호
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• pp.52-56
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• 2017

PURPOSE. Considering the importance of metal-ceramic bond, the present study aimed to compare the bond strength of ceramics to cobalt-chrome (Co-Cr) alloys made by casting and selective laser melting (SLM). MATERIALS AND METHODS. In this in-vitro experimental study, two sample groups were prepared, with one group comprising of 10 Co-Cr metal frameworks fabricated by SLM method and the other of 10 Co-Cr metal frameworks fabricated by lost wax cast method with the dimensions of $0.5{\times}3{\times}25\;mm$ (following ISO standard 9693). Porcelain with the thickness of 1.1 mm was applied on a $3{\times}8-mm$ central rectangular area of each sample. Afterwards, bond strengths of the samples were assessed with a Universal Testing Machine. Statistical analysis was performed with Kolmogorov-Smirnov test and T-test. RESULTS. Bond strength in the conventionally cast group equaled $74.94{\times}16.06\;MPa$, while in SLM group, it equaled $69.02{\times}5.77\;MPa$. The difference was not statistically significant ($P{\leq}.05$). CONCLUSION. The results indicated that the bond strengths between ceramic and Co-Cr alloys made by casting and SLM methods were not statistically different.

• 한국분말재료학회지
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• 제29권2호
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• pp.132-151
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• 2022

The CoCrFeMnNi high-entropy alloy (HEA), which is the most widely known HEA with a single face-centered cubic structure, has attracted significant academic attention over the past decade owing to its outstanding multifunctional performance. Recent studies have suggested that CoCrFeMnNi-type HEAs exhibit excellent printability for selective laser melting (SLM) under a wide range of process conditions. Moreover, it has been suggested that SLM can not only provide great topological freedom of design but also exhibit excellent mechanical properties by overcoming the strength-ductility trade-off via producing a hierarchical heterogeneous microstructure. In this regard, the SLM-processed CoCrFeMnNi HEA has been extensively studied to comprehensively understand the mechanisms of microstructural evolution and resulting changes in mechanical properties. In this review, recent studies on CoCrFeMnNi-type HEAs produced using SLM are discussed with respect to process-induced microstructural evolution and the relationship between hierarchical heterogeneous microstructure and mechanical properties.

• 한국산학기술학회논문지
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• 제19권12호
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• pp.25-31
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• 2018

선택적 레이저 용융 (Selective Laser Melting) 기법은 금속 소재를 다루는 대표적인 3D 프린팅 기법중의 하나이다. SLM 기법으로 제작되는 구조물의 특성을 좌우하는 주요 제작 인자로는 구조물의 적층 제작 방향, 레이저 파워, 레이저 스캔 스피드 및 스캔 간격 등을 고려할 수 있다. 이번 연구에서는 AlSi10Mg 합금을 대상 소재로 하여, 인장 시편의 제작 방향, 레이저 스캔 스피드 및 스캔 간격을 변수로 하여, 인장특성 결과를 비교 분석하였다. 인장특성으로는 항복 응력, 인장강도 및 연신율을 고려하였다. 시험결과로부터, 인장 시편의 제작 방향 기준으로 0도, 45도, 90도 순서로 항복 응력 값이 낮아짐을 확인하였다. 레이저 스캔 스피드 기준으로는 1870mm/min에서 가장 큰 항복 응력값을 보였으며, 스캔 스피드가 낮아질수록 항복 응력 크기도 줄어들었다. 레이저 스캔 간격 기준으로, 그 크기가 증가할수록 항복 응력값은 증가하지만, 다른 시험 기준에 비해 그 변화폭은 가장 적었다. 인장강도 및 연신율은 시험조건에 따른 명확한 경향성을 파악하기 어려웠다.

• 대한치과기공학회지
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• 제45권1호
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• pp.1-7
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• 2023

Purpose: To evaluate the marginal and internal fit of metal coping fabricated by a metal three-dimensional (3D) printer that uses selective laser melting (SLM). Methods: An extraoral scanner was used to scan a die of the prepared maxillary right first molar, and the coping was designed using computer-aided design software and saved as an stereo lithography (STL) file. Ten specimens were printed with an SLM-type metal 3D printer (SLM group), and 10 more specimens were fabricated by casting the castable patterns output generated by a digital light processing-type resin 3D printer (casting the 3D printed resin patterns [CRP] group). The fit was measured using the silicon replica technique, and 8 points (A to H) were set per specimen to measure the marginal (points A, H) and internal (points B~G) gaps. The differences among the groups were compared using the Mann-Whitney U-test (α=0.05). Results: The mean of marginal fit in the SLM group was 69.67±18.04 ㎛, while in the CRP group was 117.10±41.95 ㎛. The internal fit of the SLM group was 95.18±41.20 ㎛, and that of the CRP group was 86.35±32 ㎛. As a result of statistical analysis, there was a significant difference in marginal fit between the SLM and CRP groups (p<0.05); however, there was no significant difference in internal fit between the SLM group and the CRP group (p>0.05). Conclusion: The marginal and internal fit of SLM is within the clinically acceptable range, and it seems to be applicable in terms of fit.

• 한국분말재료학회지
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• 제25권6호
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• pp.475-481
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• 2018

Selective laser melting (SLM), a type of additive manufacturing (AM) technology, leads a global manufacturing trend by enabling the design of geometrically complex products with topology optimization for optimized performance. Using this method, three-dimensional (3D) computer-aided design (CAD) data components can be built up directly in a layer-by-layer fashion using a high-energy laser beam for the selective melting and rapid solidification of thin layers of metallic powders. Although there are considerable expectations that this novel process will overcome many traditional manufacturing process limits, some issues still exist in applying the SLM process to diverse metallic materials, particularly regarding the formation of porosity. This is a major processing-induced phenomenon, and frequently observed in almost all SLM-processed metallic components. In this study, we investigate the mechanical anisotropy of SLM-produced 316L stainless steel based on microstructural factors and highly-oriented porosity. Tensile tests are performed to investigate the microstructure and porosity effects on mechanical anisotropy in terms of both strength and ductility.

• 한국분말재료학회지
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• 제30권5호
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• pp.431-435
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• 2023

An irradiation hardening of Inconel 718 produced by selective laser melting (SLM) was studied based on the microstructural observation and mechanical behavior. Ion irradiation for emulating neutron irradiation has been proposed owing to advantages such as low radiation emission and short experimental periods. To prevent softening caused by the dissolution of γ' and γ" precipitates due to irradiation, only solution annealing (SA) was performed. SLM SA Inconel 718 specimen was ion irradiated to demonstrate the difference in microstructure and mechanical properties between the irradiated and non-irradiated specimens. After exposing specimens to Fe³⁺ ions irradiation up to 100 dpa (displacement per atom) at an ambient temperature, the hardness of irradiated specimens was measured by nano-indentation as a function of depth. The depth distribution profile of Fe³⁺ and dpa were calculated by the Monte Carlo SRIM (Stopping and Range of Ions in Matter)-2013 code under the assumption of the displacement threshold energy of 40 eV. A transmission electron microscope was utilized to observe the formation of irradiation defects such as dislocation loops. This study reveals that the Frank partial dislocation loops induce irradiation hardening of SLM SA Inconel 718 specimens.

• 한국주조공학회지
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• 제39권6호
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• pp.110-115
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• 2019

Recently, various studies have been conducted on additive manufacturing technology developed using metal materials. In this study, a numerical analysis was introduced to analyze the effects of the thermal deformation and residual stress which arise during the SLM (selective laser melting) manufacturing process. A phase-transformation mechanism is implemented with the use of the Ti-6Al-4V material, in which a solid-state phase transformation (SSPT) can be induced during a numerical analysis. In this case, the phase of the Ti-6Al-4V material changes from a powder to a solid state and then to the Martensite phase in sequence during heating and cooling steps. The numerical analysis during the SLM process was verified by comparing the results of tensile tests with those from the numerical analysis based on the SSPT material properties.

• 구강회복응용과학지
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• 제37권1호
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• pp.39-47
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• 2021

의치의 금속구조물을 selective laser melting을 통하여 제작하는 경우 기존의 제작 방식에 비해 여러 기공 과정이 생략되어 시간이 절약되고 간편해진다. 또한 균질한 밀도의 금속구조물을 얻을 수 있어 우수한 기계적 성질, 특히 피로 파절에 대한 높은 저항성을 기대할 수 있다. 본 증례에서는 부분 무치악 환자에서 기존의 방식으로 최종인상을 채득하여 주모형을 제작하였고 이를 스캔하여 데이터화 하였다. 스캔 데이터 상에서 금속구조물을 디자인한 뒤 selective laser melting 방식으로 가철성 국소의치를 제작하였으며 기능적 및 심미적으로 만족스러운 결과를 보였기에 이를 보고하는 바이다.

• 한국분말재료학회지
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• 제29권1호
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• pp.1-7
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• 2022

This study investigates the effect of process stopping and restarting on the microstructure and local nanoindentation properties of 316L stainless steel manufactured via selective laser melting (SLM). We find that stopping the SLM process midway, exposing the substrate to air having an oxygen concentration of 22% or more for 12 h, and subsequently restarting the process, makes little difference to the density of the restarted area (~ 99.8%) as compared to the previously melted area of the substrate below. While the microstructure and pore distribution near the stop/restart area changes, this modified process does not induce the development of unusual features, such as an inhomogeneous microstructure or irregular pore distribution in the substrate. An analysis of the stiffness and hardness values of the nano-indented steel also reveals very little change at the joint of the stop/restart area. Further, we discuss the possible and effective follow-up actions of stopping and subsequently restarting the SLM process.

• The Journal of Advanced Prosthodontics
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• 제13권5호
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• pp.333-342
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• 2021

PURPOSE. To evaluate the impact of five different tooth preparation designs on the marginal and internal fit discrepancies of cobalt-chromium (CoCr) crowns produced by computer-aided designing (CAD) and selective laser melting (SLM) processes. MATERIALS AND METHODS. Five preparation data were constructed, after which design crowns were obtained. Actual crowns were fabricated using an SLM process. After the data of actual crowns were obtained with structural light scanning, intaglio surfaces of the design crown and actual crown were virtually superimposed on the preparation. The fit-discrepancies were displayed with colors, while the root means square was calculated and analyzed with one-way analysis of variance (ANOVA), Tukey's test or Kruskal-Wallis test (α = .05). RESULTS. The marginal or internal color-coded images in the five design groups were not identical. The shoulder-lip and sharp line angle groups in the CAD or SLM process had larger marginal or internal fit discrepancies compared to other groups (P < .05). In the CAD process, the mean marginal and internal fit discrepancies were 10.0 to 24.2 ㎛ and 29.6 to 31.4 ㎛, respectively. After the CAD and SLM processes, the mean marginal and internal fit discrepancies were 18.4 to 40.9 ㎛ and 39.1 to 47.1 ㎛, respectively. The SLM process itself resulted in a positive increase of the marginal (6.0 - 16.7 ㎛) and internal (9.0 - 15.7 ㎛) fit discrepancies. CONCLUSION. The CAD and SLM processes affected the fit of CoCr crowns and varied based on the preparation designs. Typically, the shoulder-lip and sharp line angle designs had a more significant effect on crown fit. However, the differences between the design groups were relatively small, especially when compared to fit discrepancies observed clinically.