Mechanical Property Comparison of Ni–Cr–Mo Alloys Fabricated via One Conventional and Two New Digital Manufacturing Techniques

Kyung-Ran Yang,Tae-Yub Kwon,Takao Hanawa,Min-Ho Hong,Bong-Ki Min

doi:10.3390/app11199308

Abstract

This study compared the microstructures and mechanical properties of nickel–chromium–molybdenum (Ni–Cr–Mo) alloys prepared from a single alloy with an identical composition using two new digital processes (selective laser melting (SLM) and soft metal milling (SMM)) and conventional lost-wax casting (LWC). Disc specimens were used to study the microstructures via various analytical methods, while dumbbell-shaped specimens were subjected to tension to determine the mechanical properties (n = 6). The SLM and SMM alloys showed a higher number of large and small pores, respectively, than the LWC alloy. A face-centered cubic (γ)-phased matrix was indexed for all three resultant alloys. The SLM and SMM alloys also showed more homogeneously distributed elements and finer grains (in particular, ultrafine grains in the SLM alloy) when compared to the LWC alloy. Meanwhile, the LWC alloy showed a statistically higher yield strength than the other two alloys (p < 0.001). Notwithstanding, all three resultant Ni–Cr–Mo alloys satisfied the ISO 22674 standard criteria for type 5 materials (yield strength: >500 MPa; percentage elongation: >2%; and elastic modulus: >150 GPa).

Highlights

In the dental field, metal-ceramic prostheses are still broadly used in fixed prosthodontics, mainly due to their favorable aesthetic and mechanical properties [1]
A high number of large and small pores were evenly distributed inside the selective laser melting (SLM) and soft metal milling (SMM) alloys, respectively
The OM images of the Ni–Cr–Mo alloys are shown in Figure 3, where the results are comparable to the μCT results (Figure 2)

Summary

Introduction

Metal-ceramic prostheses are still broadly used in fixed prosthodontics, mainly due to their favorable aesthetic and mechanical properties [1]. The metallic frameworks fabricated by dental laboratories are conventionally prepared using the lostwax casting (LWC) method [2]. The dental alloys used for casting are generally divided into noble- and base-metal alloys, where cobalt–chromium (Co–Cr) and nickel–chromium (Ni–Cr) alloys are the most commonly used base-metal alloys [2]. Cobalt–chromium (Co–Cr) alloys tend to be preferred over Ni–Cr alloys, especially for. Their high melting ranges make manipulation difficult; the dark oxide layer poses an esthetic issue, and their thermal expansion coefficients make them less compatible than Ni–Cr alloys with the veneering porcelain [3,4]. Co is known to be the second most common metal allergen [3]

Methods

Results

Conclusion