Ni and Cu solubilities in cast nickel-based alloys: the addition of aluminium

Abstract

The corrosive-resistance of dental 30Ni-30Cu40Mn-based alloy systems was improved by a single additive element (either aluminum, A1 or tin, Sn), or additive compound (Al-indium (In); melting temperature, 637°C; Showa Denko Co, Tokyo), or A1-Sn (630 °C), or A l In -Sn (630 °C) [1]. The other compound Al-silicon (Si); 650 °C, or phosphate-iron (P-Fe; 1262 °C), or calcium-siliconcarbon (Ca-Si-C; 1180 °C) was also added to each parent Ni-Cu-Mn-based alloy to decrease the solubility of Ni and Cu [2]. In their alloys including 5, or 10wt% A1 in the parent alloy, dendrite structure changed more remarkably than the alloys including Sn, or Al-In, or A1-Sn. The addition of AI with a low-fusing temperature of 660 °C to the parent Ni-Cu-Mn-based alloys effectively improved the cast microstructure, so the effect of A1 on the corrosive-resistant structure and Ni and Cu solubilities should be examined for the other Ni-Cu-Mn-based alloys. Thus, it was decided to examine the amount of Ni and Cu solubility in Ni-Cu-Mn-based alloy systems to develop dental casting materials. Experimental Ni-Cu-Mn-based alloys (A1, 20Ni-40Cu-40Mn (970°C as liquidus fusion temperature); A2, 30Ni-30Cu-40Mn (1000°C); A3, 30Ni-40Cu30Mn (1050 °C); A4, 40Ni-30Cu-30Mn (1075 °C); A5, 50Ni-30Cu-20Mn (1160°C); A1A, 30Ni30Cu-35Mn-5A1 (9850C); A4A, 38Ni-28.5Cu28.5Mn-5A1 (1060 °C); A5A, 47.5Ni-28.5Cu19Mn-5A1 (1140 *C), and two commercial 84Ni9Cr alloys including other additives (NCR; Shofu Inc, Kyoto, 1310 °C) and 32Ni-23Cu-25Mn-10Cr-7Ge alloy (NCM; Sankin Ind, Tokyo, 965 °C). Alloy systems were formulated by vacuum melting as in previous studies [1-3]. The alloys were cast into phosphate-bonded investment (Univest Nonprecious Investment, Shofu Inc) using a centrifugal casting machine (Castron 8; Yoshida Co, Tokyo). Corrosive tests (37 *C; 3 days) were conducted in low pH solution such as 1% lactic acid (pH = 2.3) [4-8], and a solubility test of Ni, or Cu from the Ni-based samples was also performed in 1% lactic acid solution [2, 6, 8-10]. Corroded structures in Ni-based alloys were observed optically. All experimental specimens were 2.5 mm thick, had a surface area of 3.0 cm ~ and were ground on silicon carbide paper through 600 grit and finally polished by alumina powder with 0.5/xm particle size. Table I indicates the amount of Ni and Cu solubility in 1% lactic acid solution (pH = 2.3), TABLE I Solubility of Ni and Cu at immersion test (1% lactic acid solution; 3 days).