The conditions of cathodic charging, gaseous hydrogen environment, and loading for which a TRIP steel mey or may not be susceptible to hydrogen embrittlement were investigated. In the austenitic state, the TRIP steel appeared to be relatively immune to hydrogen embrittlement. It was shown that it is the strain-induced martensitic phase, a', which is embrittled. In TRIP steel single-edge-notch specimens under fixed loads in gaseous hydrogen, slow crack growth occurs when the stress intensity level exceeds a threshold level of about 25 ksi-in. 1 / 2 and the growth rate varies approximately as the 2.5 power of the stress intensity level. The activation energy for this slow crack growth was found to be about 10,000 cal/g-atom, the approximate activation for hydrogen diffusion in martensite. Thus it was concluded that slow crack growth in TRIP steel loaded in gaseous hydrogen involves the diffusion of hydrogen through the a' phase. .

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This paper presents an experimental study of copper dissolution in molten tin and tin-silver (Sn-Ag) solders and the formation and presence of the Cu-Sn intermetallic compound at solder/copper interfaces. During the experiments, copper (99.9% pure) samples, coated with a RMA flux, were dipped vertically in a molten solder for different time periods ranging from 5 seconds to 10 minutes. The molten solder was maintained at temperatures of 232°C, 250°C and 300°C for pure tin and 221°C, 250°C, and 300°C for Sn-3.5%Ag respectively. The samples were then cut, cleaned and cold mounted in epoxy at ambient temperature. Mechanical grinding, finish polishing, etching, and optical metallographic procedures were utilized for examining the microstructures of the polished and etched samples. The average thickness of the intermetallic compound and the amount of copper dissolved was determined. Experimental results indicate the temperature of molten solder to control the rate of dissolution of copper and the formation and presence of intermetallic compounds at the interfaces. At a given temperature of the solder temperature, the rate of dissolution of copper in the solder revealed a rising trend with an increase in dwell time of copper in the solder. For short contact time periods, the dissolution rate is low and the thickness of the intermetallic compound is small. With an increase in dwell time, the dissolution rate of copper rapidly increases and eventually reaches a plateau. Initiation of dissolution of copper causes a layer of the Sn-Cu intermetallic compound to form around the copper substrate. This in turn prevents direct contact of the copper substrate with the molten solder. The rate of formation of the layer of intermetallic compound reveals a similar trend. Based on experimental results, the kinetic parameters involved in governing the growth of the intermetallic were determined for the two solders. The parameters can be used to estimate the kinetics of copper dissolution and intermetallic compound formation during soldering.