Hideaki Tsukamoto

The influence of solder composition on the impact strength of lead-free solder ball grid array joints

This study aims to investigate the shear and tensile impact strength of solder ball attachments. Tests were conducted on Ni-doped and non-Ni-doped Sn–0.7wt.% Cu, Sn–37wt.% Pb and Sn–3.0wt.% Ag–0.7wt.% Cu solder ball grid arrays (BGAs) placed on Cu substrates, which were as-reflowed and aged, over a wide range of displacement rates from 10 to 4000 mm/s in shear and from 1 to 400 mm/s in tensile tests. Ni additions to the Sn–0.7wt.% Cu solders has slowed the growth of the interface intermetallic compounds (IMCs) and made the IMC layer morphology smooth. As-reflowed Ni-doped Sn–0.7wt.% Cu BGA joints show superior properties at high speed shear and tensile impacts compared to the non-Ni-doped Sn–0.7wt.% Cu and Sn–3.0wt.% Ag–0.7wt.% Cu BGAs. Sn–3.0wt.% Ag–0.7wt.% Cu BGAs exhibit the least resistance in both shear and tensile tests among the four compositions of solders, which may result from the cracks in the IMC layers introduced during the reflow processes.

Formation and Mechanical Properties of Intermetallic Compounds in Sn-Cu High-Temperature Lead-Free Solder Joints

High-temperature lead-free solders are important materials for electrical and electronic devices due to increasing legislative requirements that aim at reducing the use of traditional lead-based solders. For the successful use of lead-free solders, a comprehensive understanding of the formation and mechanical properties of Intermetallic Compounds (IMCs) that form in the vicinity of the solder-substrate interface is essential. In this work, the effect of nickel addition on the formation and mechanical properties of Cu6Sn5 IMCs in Sn-Cu high-temperature lead-free solder joints was investigated using Scanning Electron Microscopy (SEM) and nanoindentation. It was found that the nickel addition increased the elastic modulus and hardness of the (Cu, Ni)6Sn5. The relationship between the nickel content and the mechanical properties of the IMCs was also established.

Formation behavior of continuous graded composition in Ti-ZrO 2 functionally graded materials fabricated by mixed-powder pouring method

A mixed-powder pouring method has been proposed to fabricate functionally graded materials (FGMs) with the desired compositional gradient. The experimental procedure involves preparation of mixed powders consisting of more than two types of particles with different size and/or density, which exhibit different velocities in suspension and sedimentation to form the green body under gravity conditions. The green body was sintered by a spark plasma sintering (SPS) method. The initiation of the particle settlement was precisely controlled by using crushed ice as the suspension medium. Ti-ZrO2 FGMs were fabricated, in this study, using different sizes of ZrO2 and Ti particles. Vickers hardness confirmed the compositional gradient in the fabricated FGMs. A numerical simulation was also carried out to analyze the particle movement inside the suspension medium during the formation process and predict compositional gradient in the FGMs.

Microstructure and Mechanical Properties of Ti-ZrO2 Composites Fabricated by Spark Plasma Sintering

This study aims to investigate the microstructure and mechanical properties of Ti-ZrO2 composites and ZrO2/Ti functionally graded materials (FGMs) fabricated by spark plasma sintering (SPS). SPS has been conducted in a vacuum at 1400 oC under the uniaxial pressure of 30 MPa. Mechanical properties such as hardness and elastic modulus of Ti-ZrO2 composites have been systematically investigated using micro-Vickers and nanoindentation. The experimental results demonstrate that the mechanical properties of Ti are dramatically improved by an addition of small amount of ZrO2. There is almost no effect from the presence of Y2O3 in ZrO2 on the hardness of Ti-ZrO2 composites. ZrO2/Ti FGMs have been successfully fabricated, and mechanical properties of the FGMs have been examined.

Creep Analysis of Functionally Graded Material Thick-Walled Cylinder

In this paper, creep analysis for a thick-walled cylinder made of functionally graded materials (FGMs) subjected to thermal and internal pressure is carried out. The structure is replaced by a system of discrete rectangular cross-section ring elements interconnected along circumferential nodal circles. The property of FGM is assumed to be continuous function of volume fraction of material composition. The creep behavior of the structures is obtained by the use of an incremental approach. The obtained results show that the property of FGM significantly influences the stress distribution along the radial direction of the thick-walled cylinder as a function of time.

Micromechanical study on high-temperature behavior of ZrO2 particle-dispersed Ni composites

This paper aims to investigate high temperature behavior of ZrO2 particle-dispersed Ni composites. The tension-compression tests under constant stress rates as well as creep tests including stress-dip tests were performed using a high-temperature material testing set up, which consists of an electric-hydraulic fatigue testing machine, electric furnace and extensometer with a laser sensor. ZrO2 particle-dispersed Ni composites were fabricated by using the powder metallurgical methods. The results obtained from the experimental study show that ZrO2 particles remarkably strengthen the composite and there exists a reasonable correlation between the tensioncompression stress-strain relation and the creep behavior. In addition, the creep behavior has been examined based on the micromechanical concept, which takes into account the diffusional mass flow at the interface between the particles and matrix. Some numerical analysis based on this concept demonstrates that even a little amount of ZrO2 particles can effectively increase the creep resistance of the composites

Design of ZrO2/Ti Functionally Graded Thermal Barreir Coatings Based on a Nonlinear Micromechanical Approarch

This study presents a design process of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a mean-field nonlinear micromechanical approach developed by Tsukamoto [1], which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. The effect of compositional gradations on micro-stress states in the FG TBCs has been examined. The suitable compositional gradations have been proposed for typical thermo-mechanical boundary conditions in terms of thermal-stress relaxations, thermal-shielding and light-weight characteristics.

Micromechanics-based Study on Thermo-mechanical Behavior of ZrO2/Ti Functionally Graded Materials

The aim of this study is to investigate thermo-mechanical response of ZrO 2 /Ti functionally graded materials (FGMs) fabricated by spark plasma sintering (SPS) based on a mean-field micromechanics model, which takes account of micro-stress relaxation due to interfacial diffusion between ceramic and metal phases as well as creep of both phases. A resistance to cyclic thermal shock loadings of FGMs with different compositional gradation patterns including Ti-rich, linear and ZrO 2 -rich gradation patterns has been investigated. The results demonstrate that Ti-rich FGMs show superior properties among the tested FGM samples. Mean-field micromechanics-based examinationsreveal that the range and ratio of thermal stresses in ZrO 2 surface layers in FGMs can affect cyclic thermal shock fracture behaviour but not mean thermal stresses. Creep of ZrO 2 have a large influence on dependence of the range and ratio of thermal stresses in ZrO 2 surface layers on compositional gradation patterns in the FGMs.

Effect of Creep on Thermal Stresses in ZrO2/Ti Functionally Graded Thermal Barrier Coatings

This study numerically investigates the effect of creep on thermal stress states and design of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a mean-field nonlinear micromechanical approach, which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. The effect of creep on micro-stress states in the FG TBCs has been examined in terms of the compositional gradation patterns. The suitable compositional gradation patterns have been proposed for typical thermo-mechanical boundary conditions with different creep abilities of constitute phases in the FG TBCs.

Effect of compositional gradient on mechanical properties in aluminum/duralumin multi-layered clad structures

This study aims to investigate the effect of compositional gradient on nano-, micro- and macro-mechanical properties in aluminum (A1050)/ duralumin (A2017) multi-layered clad structures fabricated by hot rolling. Such multilayered clad structures are possibly adopted to a new type of automobile crash boxes to effectively absorb the impact forces generated when automobiles having collisions. 2- and 6-layered clad structures with asymmetric lay-ups from one side of aluminum to another side of duralumin have been fabricated, which have been suffering three different heattreatments such as (1) as-rolled (no heat-treatment), (2) annealed at 400°C and (3) homogenized at 500°C followed by water quenching and aging (T4 heat treatment). For nano- and micro-scale mechanical properties proved by nanoindentation, higher hardness and elastic modulus correspond to higher Cu content at the interface in annealed and aged samples. For macro-scale mechanical properties, internal friction of 2-layered clad structures is higher than that of 6-layered clad structures in any heat-treatment samples. Deep drawing formability of annealed samples is considerably high compared to as-rolled and aged ones.