Cu3Sn-microporous copper composite joint for high-temperature die-attach applications

Purpose The purpose of this paper is to design a novel die-attach composite joint for high-temperature die-attach applications based on transient liquid phase bonding. Moreover, the microstructure, shear strength, electrical property, thermal conductivity and aging property of the composite joint were investigated. Design/methodology/approach The composite joint was made of microporous copper and Cu3Sn. Microporous copper was immersed into liquid Sn to achieve Sn-microporous copper composite structure for die attachment. By the thermo-compression bonding, the Cu3Sn-microporous copper composite joint with a thickness of 100 µm was successfully obtained after bonding at 350 °C for 5 min under a low pressure of 0.6 MPa. Findings After thermo-compression bonding, the resulting interconnection could withstand a high temperature of at most 676 °C, with the entire Sn transforming into Cu3Sn with high remelting temperatures. A large shear strength could be achieved with the Cu3Sn-microporous copper in the interconnections. The formed bondlines demonstrated a good electrical and thermal conductivity owing to the large existing amount of copper in the interconnections. Furthermore, the interconnection also exhibited excellent reliability under high temperature aging at 300 °C. Originality/value This die-attach composite joint was suitable for power devices operating under high temperatures or other harsh environments.

Influence of the Evolution of 9CrMoCoB Steel Precipitates on the Microstructure and Mechanical Properties during High-Temperature Aging

In this study, the short-term aging was carried out to reveal the evolution of precipitates and mechanical properties of heat resistant 9CrMoCoB steel during the early creep, replacing the conventional creeping. The tempered martensite lath structure (TMLS) and precipitates were observed in the as-aged 9CrMoCoB steel. TMLS in the matrix underwent a transition to the polygonal ferrite after aging only for 300 h. In comparison, the mean diameter of the precipitates increased from 183 to 267 nm after aging at 650 °C for 300 h. Also, the mean diameter of the precipitates increased from 183 to 302 nm at 700 °C. The room-temperature and high-temperature strength of 9CrMoCoB steel decreased after high-temperature aging, which may be mainly due to precipitates coarsening. Many M23C6 phases precipitate in the prior austenite grain boundary (PAGB) and lath boundary. After aging 100 h, TMLS transformed into polygonal ferrite, and the size of the precipitate at the subgrain boundary was about 100 nm, while after 300 h of high-temperature aging, large precipitates appear (400 nm) in the matrix. After 200 h of high-temperature aging, the obvious growth of precipitates on the PAGB and lath boundary weakens the pinning effect on the PAGB and martensite lath boundary and accelerates the transformation of microstructure and mechanical properties.

Thermal Analysis and Selected Properties of CuNi2Si Alloy Used for Railway Traction

This paper investigates the effect of high-temperature aging (600 °C and 650 °C) on the microstructure and functional properties of copper CuNi2Si alloy. The paper also presents the results of elastomeric tests performed by means of the Gleeble 3800 heat and plastic treatment simulator, as well as DTA (Differential Thermal Analysis) analysis carried out for the investigated alloy aged for 1, 2, 4 and 7 h. Corrosion resistance tests were performed by means of the potentiodynamic method with Atlas Sollich Atlas 0531 potentiostat/galvanostat in a 3% sodium chloride solution. Based on the tribological tests, it was confirmed that the CuNi2Si alloy was solution heat treated from the temperature of 1000 °C and gradually aged at the temperature of 600 °C and 650 °C for 1–7 h, characterized by a stable wear resistance. The alloy aged at the temperature of 600 °C was characterized by a lower mass loss compared to the one aged at 650 °C. Based on the DTA analysis, it was found that for the alloy aged for 2, 4 and 7 h, at the temperatures of 401 °C, 411 °C and 412 °C, respectively, the decomposition of a supersaturated solid solution took place by spinodal transformation accompanied by a sequence of phase transitions DO22 [(Cu, Ni)3Si],→ δ-Ni2Si → (Cu, Ni)3Si. The results of these investigations have proved that the CuNi2Si alloy can be widely used for electric traction. The use of alloys that replace elements made entirely of copper and, in this way influencing its lower demand, is in line with the global policy of economical management of natural resources.

Thermo-oxidative aging and thermal cycling of PETI-340M composites

Polyimide composites (PETI-340M) were fabricated and subjected to high-temperature aging and thermal cycling to evaluate resistance to degradation. Mechanical-degradation mechanisms and kinetics depended on aging temperature. Aging at 232°C resulted in strength loss due to polymer degradation, while intra-tow cracking was the dominant mechanism during aging at 288°C. Composite panels subjected to thermal-cycling fatigue (−54°C to 232°C) retained mechanical properties without microcracking. However, in regions containing pre-existing fabrication-induced defects (primarily voids), intra-tow microcracks were observed after thermal cycling. Unlike some polyimide composites (PMR-15), oxidative aging effects during thermal cycling were negligible. The thermo-oxidative stability and the retention of mechanical performance after thermal cycling indicates potential for long-term, high-temperature structural applications.

The Features of Martensitic Transformation in 12% Chromium Ferritic–Martensitic Steels

An anomaly in martensitic transformation (the effect of martensitic two-peak splitting in the temperature-dependent thermal expansion coefficient) in complex alloyed 12% chromium steels Fe-12%Cr-Ni-Mo-W-Nb-V-B (ChS-139), Fe-12%Cr-Mo-W-Si-Nb-V (EP-823) and Fe-12%Cr-2%W-V-Ta-B (EK-181) was investigated in this study. This effect is manifested in steels with a higher degree of alloying (ChS-139). During varying temperature regimes in dilatometric analysis, it was found that the splitting of the martensitic peak was associated with the superposition of two martensitic transformations of austenite depleted and enriched with alloying elements. The anomaly was subsequently eliminated by homogenization of the steel composition due to high-temperature aging in the γ-region. It was shown that if steel is heated to 900 °C, which lies in the (α + γ) phase region or slightly higher during cooling, then the decomposition of austenite proceeds in two stages: during the first stage, austenite is diffused into ferrite with carbides; during the second stage, shear transformation of austenite to martensite occurs.