The reliability of Sn-3.0Ag-0.5Cu (SAC 305) solder joint under a broad level of drop impacts was studied. The failure performance of solder joint, failure probability and failure position were analyzed under two shock test conditions, i.e., 1000 g for 1 ms and 300 g for 2 ms. The stress distribution on the solder joint was calculated by ABAQUS. The results revealed that the dominant reason was the tension due to the difference in stiffness between the print circuit board and ball grid array, and the maximum tension of 121.1 MPa and 31.1 MPa, respectively, under both 1000 g or 300 g drop impact, was focused on the corner of the solder joint which was located in the outmost corner of the solder ball row. The failure modes were summarized into the following four modes: initiation and propagation through the (1) intermetallic compound layer, (2) Ni layer, (3) Cu pad, or (4) Sn-matrix. The outmost corner of the solder ball row had a high failure probability under both 1000 g and 300 g drop impact. The number of failures of solder ball under the 300 g drop impact was higher than that under the 1000 g drop impact. The characteristic drop values for failure were 41 and 15,199, respectively, following the statistics.

(Ti, Nb)C reinforced Fe-based laser coatings were prepared with normal and high scanning velocities of the laser beam. The distribution characteristics of reinforced particles in the coatings were investigated. The mechanical properties of coatings were tested. The results showed that the morphologies of the microstructure and the reinforced particle changed dramatically at high solidification rate due to rapid laser processing compared with that prepared by normal processing. Two kinds of particles were observed in the coating. One was (Ti, Nb)C multiple carbide particle with the size of micron and sub-micron scales, in which a mass of dislocations were found. Another was nano-sized particle including α-Fe and (Ti, Nb) C obtained by rapid solidification. The microstructure of the coatings was highly refined and a large number of twin crystals were found in matrix. The results of mechanical properties test revealed that the wear resistance of the coating was improved by rapid laser processing, compared with that of the coating prepared with normal speeds. The above-mentioned conclusion indicated that rapid laser cladding can promote not only the processing efficiency but also the mechanical properties of the coating.

The scattering of fatigue life data is a common problem and usually described using the normal distribution or Weibull distribution. For solder joints under drop impact, due to the complicated stress distribution, the relationship between the stress and the drop life is so far unknown. Furthermore, it is important to establish a function describing the change in standard deviation for solder joints under different drop impact levels. Therefore, in this study, a novel conditional probability density distribution surface (CPDDS) was established for the analysis of the drop life of solder joints. The relationship between the drop impact acceleration and the drop life is proposed, which comprehensively considers the stress distribution. A novel exponential model was adopted for describing the change of the standard deviation with the impact acceleration (0 → +∞). To validate the model, the drop life of Sn-3.0Ag-0.5Cu solder joints was analyzed. The probability density curve of the logarithm of the fatigue life distribution can be easily obtained for a certain acceleration level fixed on the acceleration level axis of the CPDDS. The P–A–N curve was also obtained using the functions μ(A) and σ(A), which can reflect the regularity of the life data for an overall reliability P.

Agglomerated TiB2 particle and network-like structure-reinforced titanium matrix composite coatings were prepared by laser cladding of the Ni + TiB2 + Ti preplaced powders on Ti-6Al-4V alloy. The network-like structure mainly consisted of NiTi and Ni3Ti. Through the experiment, it was found that the size of agglomerated particle gradually decreased with the increase of Ti content, but the number of the network-like structure first increased and then disappeared. In-situ reaction competition mechanism and the formation of network-like structure were discussed. The average micro-hardness gradually decreased with the increase of Ti content, but the average fracture toughness gradually increased. Meanwhile, the wear resistance of the coatings is higher than that of the substrate, but the wear loss of the coatings is gradually increased with the increase of Ti content.

•The formation of NbC particles with large size around Nb particles was observed.•NbCp with small size forms by the reaction of Nb, C dissolve in the molten pool.•CeO2 can reduce porosities, refine grains and improve the precipitation of NbC.•CeO2 improves the solid solubilities of solutes in Fe matrix of the coating.•CeO2 enhances the micro-hardness and diminishs its fluctuation in the coating.Over the past decade, researchers have demonstrated much interest in laser cladded metal matrix composite coatings for its good wear resistance, corrosion resistance and high temperature properties. The effects of RE on the microstructure and properties of laser coatings have also got more and more attention. In this paper, in situ Fe-NbC composite coatings with different CeO2 addition were produced on die steel by laser cladding. The formation mechanism of NbC particles was analyzed. The effects of RE on microstructure and micro-hardness of coatings were investigated. It was revealed that larger NbC particles with hard edges formed around Nb particles, and smaller flocculent NbC particles formed by the chemical reaction of Nb and solid graphite in the molten pool. CeO2 plays important roles in reducing micro-porosities, refining grains, and improving the precipitation of NbC. Therefore, the average micro-hardness and its smoothness from the top to the bottom of the coating were improved after adding CeO2.