Change in Microstructure, Mechanical Strength and Corrosion Resistance of Ti-8Mo-xNi Alloys through Various Sintering Temperatures

Abstract

In this study, three different powders are mixed and used to produce Ti-8Mo-xNi alloys in three different proportions: Ti-8Mo-4Ni, Ti8Mo-6Ni and Ti-8Mo-8Ni. The Ti-Mo-Ni alloys simultaneously undergo various vacuum sintering temperatures of 1125, 1150, 1175 and 1200 C, respectively. The experimental results show that the Ti-8Mo-8Ni alloys acquire a higher sintering density (98.9%) and hardness (52.1 HRC) after sintering at 1175 C for 1 h. However, due to the grain growth and increased amount of nickel in the Ti-8Mo-8Ni alloys, the transverse rupture strength (TRS) shows an obvious decrease (as compared with Ti-8Mo-6Ni, the TRS value decreasing from 1177 to 685 MPa). Consequently, the suitable Ni content of the Ti-8Mo-6Ni alloys which proves advantageous to the TRS results from the uniform distribution of the TiNi intermetallic compound precipitates within the β matrix. The sintered Ti-8Mo-8Ni alloys also possess the lowest corrosion current (I corr = 1.87 × 10 −7 A·cm −2) and highest polarization resistance (56084 Ω·cm 2 ) in 3.5 mass% NaCl solutions. This result con rms that sintered Ti-8Mo-8Ni alloys effectively improve corrosion resistance.

Investigation of the Microstructures, Mechanical Properties and Corrosion Behaviours of Ti-8Mo-6Ni Alloys Adding NbC PowdersviaVacuum Sintering Process

“…5a. The previous literature indicates that decreasing the porosities and increasing the density of sintered materials effectively enhances plastic deformation resistance and hardness [2,12]. In this study, the porosities decreased and the relative density increased as the sintering temperature was raised (1175 → 1225 → 1275°C), which could be the main factor in improving hardness.…”

“…Fig 2 reveals the XRD patterns of the NbC-1, NbC-3 and NbC-5 specimens after sintering at 1275°C for 1 h. Previous study indicated that the impurity concentrations of vacuum-sintered commercially pure titanium with fine grains were sufficiently low to meet the ASTM standard. It illustrates that the oxygen, nitrogen and hydrogen contents of the specimens was lower than that of ASTM (B381-10) [2,11]. As a result, the contamination levels such as oxygen, nitrogen and hydrogen can be ignored.…”

“…Previous researches have studied the phase transformations and mechanical properties of different Ti-Mo alloys, and found that the phase constitutions, elastic modulus and hardness are different for Ti-Mo alloys with different Mo contents [3,4]. It is remarkable that the Ti-8Mo exhibits the highest mechanical properties among the porous Ti-(4-10 wt%)Mo alloys [2,5]. Powder metallurgy (P/M) methods offer various types of materials with the objective of achieving higher strength, hardness and wear resistance for composite materials such as titanium-based alloys powders.…”

“…Conventional P/M involves mixing the metal powders, compacting of the mixed powders into moulds and then sintering of the compact powders under the different atmospheres [6,7]. Furthermore, our previous study has shown that the combination of these elements in a Ti-8Mo-6Ni alloy has a good balance between mechanical properties and hot workability [2].…”

“…During the past few decades, β titanium alloys have become one of the most promising candidates due to their high specific strength and good corrosion resistance [1,2]. Mo is desirable as an alloying element for the development of Ti-based biomaterials.…”