Influence of Niobium or Molybdenum Addition on Microstructure and Tensile Properties of Nickel-Chromium Alloys

Marisa Aparecida De Souza,Alfeu Saraiva Ramos,Tomaz Manabu Hashimoto,Bárbara De Oliveira Fiorin,Ana Paula Rosifini,Carlos Angelo Nunes,Carlos Antônio Reis Pereira Baptista

doi:10.3390/met9050589

Marisa Aparecida De Souza, Alfeu Saraiva Ramos + Show 5 more

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https://doi.org/10.3390/met9050589

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Abstract

This work discusses on influence of niobium or molybdenum addition on microstructure and tensile properties of NiCr-based dental alloys. In this regard, the Ni-24Cr-8Nb, Ni-22Cr-10Nb and Ni-20Cr-12Nb (wt. %) alloys produced by arc melting process. To compare the typical Ni-22Cr-10Mo dental alloy was also produced. These ternary alloys were analyzed by chemical analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive spectrometry (EDS), thermogravimetric analysis (TG), Vickers hardness and tensile tests. Although the mass losses of the samples during arc melting, the optical emission spectrometry showed that the initial compositions were kept. The Ni-22Cr-10Mo alloy produced a matrix of Niss (ss—solid solution), whereas Ni3Nb disperse in a Niss matrix was also identified in Ni-Cr-Nb alloys. Excepting for the Ni-22Cr-10Nb alloy with mass gain of 0.23%, the as-cast Ni-Cr alloys presented mass gains close to 0.4% after heating up to 1000 °C under synthetic airflow. The hardness values, the modulus of elasticity, yield strength and ultimate tensile strength have enhanced, whereas the ductility was reduced with increasing niobium addition of up to 12 wt.-%.The Ni-22Cr-10Mo alloy presented an intergranular fracture mechanism containing deep dimples and quasi-cleavage planes, whereas the shallow dimples were identified on fracture surface of the as-cast Nb-richer Ni-Cr alloys due to the presence of higher Ni3Nb amounts.

Highlights

As-cast nickel-chromium (Ni-Cr) and nickel-chromium-molybdenum (Ni-Cr-Mo) based alloys are applied in dentistry to partial removable prosthesis since 1930 because of their excellent characteristics, such as corrosion resistance and mechanical properties, compared with the more expensive gold-based alloys
Typical chemical compositions of different commercial Ni-Cr alloys used for metal-ceramic restorations presented the Cr and Mo contents varying between 18.5–20.4 wt. % and 4.2–9.5 wt. %, respectively [5]
In accordance with the phase diagrams of the nickel-chromium [7] and nickel-molybdenum [8] systems, the adopted chromium and molybdenum amounts in these commercial Ni alloys are located in regions of Ni solid solutions, respectively

Summary

Introduction

As-cast nickel-chromium (Ni-Cr) and nickel-chromium-molybdenum (Ni-Cr-Mo) based alloys are applied in dentistry to partial removable prosthesis since 1930 because of their excellent characteristics, such as corrosion resistance and mechanical properties, compared with the more expensive gold-based alloys. The less expensive and lighter Ni-Cr alloys with high elastic module (170–190 GPa) have been developed for producing metal-ceramic restorations, intra-radicular pins, crowns and removable partial prosthesis [1,2,3]. In these alloys, the chromium is responsible for the formation of an outer protective oxide layer [4]. In accordance with the phase diagrams of the nickel-chromium [7] and nickel-molybdenum [8] systems, the adopted chromium and molybdenum amounts in these commercial Ni alloys are located in regions of Ni solid solutions, respectively. The use of metal matrix-intermetallic composites can improve the need flexural strength for dentistry devices [9]

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