Wei Xicheng

Tensile Fracture Behavior of Sn-3.0Ag-0.5Cu Solder Joints on Copper

Microstructural features and tensile properties of Sn-3.0Ag-0.5Cu solder joints on copper with various aging time at 150degC were examined. The solder inner and solder/Cu interface were analyzed by SEM to identify the fracture location, morphology and compositions. The study has showed, the tensile fracture strength of the solder joints decreases with the increased aging time, and the crack initiates mostly at the interfaces between the solder and IMC layer or/and IMC and IMC layer. The morphology of fracture surface changes from dimple-like to cleavage-like surfaces. The needle-like or block-like interfacial IMCs form at the interface of Cu/solder and grow into the solder matrix. Otherwise, the Kirkendall voids can be observed in the multilayer structure close to the copper substrate. These voids have probably a detrimental effect on the tensile fracture behavior.

Research on Friction-Coatings with Activated Ultra-Thick Tin-Base

This paper introduced a new Nanometer-Tin lubricating additive. Through the friction testing on an improved testing machine, the Nanometer additive with different contents used in Steel-Copper Tribo-pair has been investigated by analyzing the surface elements with AES and measuring the thickness and element distribution of the coating with SEM. The result shows that the weight of copper sample has obviously increased, and the ultra-thick friction coating (10μm−20μm), has formed on the surface of the copper sample. The experiment proved that the high concentrated Sn coating has good frictional properties. Therefore, the researching results possess significance to self-repair in wearing for mechanical system.

Study on the microstructure and electrical properties of boron and sulfur codoped diamond films deposited using chemical vapor deposition

The atomic-scale microstructure and electron emission properties of boron and sulfur (denoted as B-S) codoped diamond films grown on high-temperature and high-pressure (HTHP) diamond and Si substrates were investigated using atom force microscopy (AFM), scanning tunneling microscopy (STM), secondary ion mass spectroscopy (SIMS), and current imaging tunneling spectroscopy (CITS) measurement techniques. The films grown on Si consisted of large grains with secondary nucleation, whereas those on HTHP diamond are composed of well-developed polycrystalline facets with an average size of 10-50 nm. SIMS analyses confirmed that sulfur was successfully introduced into diamond films, and a small amount of boron facilitated sulfur incorporation into diamond. Large tunneling currents were observed at some grain boundaries, and the emission character was better at the grain boundaries than that at the center of the crystal. The films grown on HTHP diamond substrates were much more perfect with higher quality than the films deposited on Si substrates. The local I-V characteristics for films deposited on Si or HTHP diamond substrates indicate n-type conduction.

Study on the Relationship between Microstructural Change in Friction-Induced Deformation Layer and Friction Behavior of Austenitic Stainless Steel

Friction and wear behaviors of 304 metastable austenitic stainless steel (MASS) pin against DC53 disc were studied using a German SST-ST disc-on-pin tester in this paper. The tests were performed under 200, 300 and 400 N with constant sliding speed 0.2m/s. SEM, 3D profiler and XRD were employed to observe the wear morphology, detect the martensitic transformation and analyze the microstructure change of 304 MASS. The relationship between microstructural change in friction-induced deformation layer and friction behaviors of MASS was discussed. Results showed that lots of friction-induced martensite was transformed from austenite in the deformation layer of pin specimen, which volume fraction decreased with the increase of distance away from the frictional surface. Results also showed that the friction behavior of 304 MASS was influenced by phase transformation and microstructural change in the deformation layer of 304 MASS. These conclusions are significant to guiding the process design during pressing.