Grain-Size Refinements of Cu-3 mass%Ti Alloys by HDDR Treatments in Correlating with Their Electrical and Mechanical Properties

Abstract

The present paper describes the grain size refinements of Cu-3 mass%Ti alloys by hydrogen heat-treatment of so-called HydrogenationDisproportionation-Desorption-Recombination (HDDR) process. During hydrogenation process, the disproportionation reaction occurred with forming of Ti hydrides in the alloy. With decomposition of Ti hydrides by the subsequent desorption process, Ti resolved into Cu matrix. In consequence, the original solid solution phase of the alloys formed. This means that the HDDR phenomena could take place in the Cu-3 mass%Ti alloy. The grain size of the alloy is found to be about 20-50 nm after HDDR treatments such as hydrogenation treatment at 350 C under hydrogen pressure of 7.5 MPa for 48 h, followed by the hydrogen desorption treatment at 530 C for 4 h in vacuum. On the other hand, it is found that remarkable simultaneous improvements of mechanical strength of 1100 MPa and electrical properties of 21%IACS are obtained in the hydrogenated alloy.

New function of hydrogen in materials

“…For Cu solidsolution alloy in Cu-Ti system, Vegard's law could be applied, in which the lattice constants are proportional to Ti amount in fcc matrix. This reduction of lattice constants might be due to decrement of Ti content in copper-matrix, in probably forming TiH 2 during hydrogen heat-treatment [7].…”

“…However, hydrogen had been regarded as harmful element such as inducing hydrogen-embrittlement in metals. Recently, the new attempts to find the useful function of hydrogen have attracted much attentions since hydrogen introduces the unexpected function in materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The present paper reviews the useful function of hydrogen recently found in the materials, in relation to drastically increase their properties, in adding newly obtained results.…”

Simultaneous Enhancement of Electrical Conductivities and Mechanical Properties in Cu-Ti Alloy by Hydrogenation Process

“…That means all samples could hydrogenate under the condition. In our previous work, it was found that the Cu-3mass% alloy decomposed to Cu-matrix phase, Ti-hydride (TiH~2) and D1a (Cu 4 Ti) phase [11]. Figure 2 shows nominal stress of the corresponding alloys for as-rolled state, after hydrogenation or after annealing under Ar atmosphere at 350°C for 48h.…”

“…Recently, we also reported the grain size refinements of Cu-3mass%Ti alloys by hydrogen heat-treatment of HDDR process [11]. The alloy is commercially available, and has been widely used for high-strength electrical conducting materials such as lead frames and connectors.…”

“…Further detailed studies are required to clarify the reason why these conditions yielded the excellent properties. This new finding that aging of the alloys in hydrogen gives the simultaneous improvements of electrical conductivity and mechanical strength, may be applicable to the other spinodal or precipitated-hardened alloys in the future Dutkiewicz reported the existence of spinodal curve on the composition of about 2mass%Ti at 300-400°C [15] which temperature was reported as optimized hydrogenation process in Cu-3mass%Ti [11]. In the present investigation, we focused on the Ti content around spinodal composition in Cu alloy applying hydrogenation process.…”