Advanced Materials Research Vols. 126-128

Abstract: According to the morphological characteristic of the new rotor steel, the cutting temperature and cutting forces generated by milling were investigated. The cutting temperature and forces resulted in the changes of the microstructure and residual stress of the machined surface. The tensile residual stress in the machined surface was affected more remarkably by the cutting temperature than cutting forces. In the microstructure of the machined surface, the larger plastic deformation in the machined surface and martensitic damage in the subsurface were also observed, which favored the higher tensile residual stress.

Abstract: An electro-thermo coupling finite element model is developed to investigate the electromigration and electro-thermo-mechanical effects on electronic packaging. Sn4.0Ag0.6Cu (SAC405) solder ball are commonly used on POP package in this research. Current density arising in the Copper trace above SAC405 solder ball implies the hot spot where results in an electromigration along the current direction. Finite element predictions reveal the peak electro-thermo-mechanical effective stress is located at the regions where electromigration potentially occurred. Current crowding, temperature distribution and electro-thermo induced effective stress distribution are predicted. A submodel scheme is applied for evaluation of equivalent life time of solder ball. Reliability analysis on electro-thermo-mechanical for SAC405 solder ball is evaluated.

Abstract: A series of Ti/TiN multilayer films were prepared by reactive DC magnetron sputtering onto Si(111) substrates. The resistivity and optical reflectance of these thin films were measured as a function of the modulated, multilayered thickness and the number of layered structures. The resistivity decreased with increase in the number of layers in the film up to 4 layers. The reflectance in the near infrared region increased with increase in layer thickness but after a certain thickness, the change in reflectance was minimal. An optimum thickness of 25 nm for the modulated film realized a maximum of 0.829 in the near infrared reflectance. With the number of layers greater than 15, an interfacial layer of Ti2N was observed.

Abstract: Scratch experiments were performed on MgO (001) plane along different crystallographic orientations with the gradually increased forces to investigate the deformaton and damage of MgO. The normal and lateral forces during scratch, as well as the topography characteristics of the residual scratch along different crystallographic orientations were compared and analyzed. The cracks propagation around the scratch were studied. The patterns of cracks and scratches were found to be very different when scratching along different crystallographic orientations. The mechanism of cracks forming beside the scratches on single crystal MgO was discussed.

Abstract: Abesive jet machining (AJM) of silicon carbide fiber reinforced silicon carbide ceramic composite (SiC/SiC CMC) was carried out with various size of silicon carbide fine abresives. A micro indentation experiment was connected to evaluate of maerial removal mechanism by the particle impact. Results showed that the machine rate was different depending on the particle size and that inteface fracture (debonding) has influenced on the material removal mechanim. Relationship between structure scale of the SiC/SiC CMC and the impact media size was discussed.

Abstract: This paper investigates effects of particle size on heat transfer in copper powders. The understanding for thermal properties of the powder is advantageous to the advancement of the processing technologies such as laser cladding, laser sintering, powder metallurgy and its other applications. Nanosized particles possess characteristic physical and chemical properties different from those of bulk materials due to the confinement of electrons, excitons, and photons into small volumes. Therefore it is valuable to discuss the thermal behaviours of powders constituted by nanometer-sized particles. The powder is wrapped up in the slender tube. One end of the slender tube filled with powder is connected to the low constant-temperature reservoir and the other end is kept at room temperature. The temperature histories at the 1cm location of the slender tube from the low constant-temperature reservoir are recorded using thermal couples. Powders of particles with the sizes 50nm and 5000nm are employed in this experiment. The results show that the thermal diffusion in the 50nm Cu powder is faster than that in the 5000nm Cu powder.

Abstract: Human bone fracture associated with osteoporosis was hypothesized to be related to the alteration of mechanical properties in bones. In this work, cortical and trabecular bones from human femoral heads were studied. Bone samples of eight female and four male patients, with ages varying from 37 to 93 years, were collected from total hip replacement surgery. Reduced modulus (Er) and hardness (H) of osteons, interstitial lamellae and trabeculae were characterized by nanoindentation. The results showed both the reduced modulus and hardness of the interstitial lamellae were significant higher than those of osteons and trabeculae. Though there was no significant difference in microstructures in the Group A (age < 60 years) and B (age > 60 years), the Group B bones demonstrated to be stiffer.

Abstract: The wear experimental project on contact pressure, sliding speed and surface hardness was instituted by the uniform design method, the wear properties were investigated on a vertical universal friction/wear tester, the worn surfaces of specimens were observed by scanning electron microscope (SEM). The wear rate predication model was established by polynomial regression analysis, and the goodness of fit and the significance of influencing factors was verified. The results showed that the experimental efficiency was evidently increased, and the experimental cycle was shortened by the uniform design. It is found that the wear rate predication model established is reasonable and valid, and the impact of three factors on the wear rate is coupling effect. The main wear mechanism is abrasive wear and adhesive wear.

Abstract: Ceramic coatings have been widely used in cutting tools and various machine parts. Even though high strengths have been obtained in most ceramic coatings, it has also been shown that ceramic coatings undergo extensive plastic deformation during scratch and wear tests. Therefore, it is essential to understand the plastic flow and related friction and wear behaviour. Reciprocating multipass wear tests have been carried out on chemical vapor deposition (CVD) TiC coatings. Obvious plastic flow was observed on the rough surface of CVD TiC ceramic coatings in the first sliding, due to the extremely high contact pressure developed on the contact asperities. However, shake down may be quickly reached after several subsequent traverses. In further repeated traverses, the plastic-elastic flow accumulates residual strain energy to the point where cracking, microbuckling, and microflaking may occur along the elastic-plastic interfaces behind the indenter. The new rough surface will appear after the detachment of the heavily strained plate-like wear debris. The repeated sliding allows the process- “plastic flow of asperities - flatten the surface and shake down - microbuckling and detachment of strained layer” to continue until the coating is totally worn out.

Abstract: The wear volume is obtained by means of experiment and the wear random process model is established according to the result. The Carbon steel material is used and the samples are grouped five after surface treatment, each group tests six times under the same condition. The wear volume under each wear time shows big dispersion. The additional study indicates that the sample has the large wear volume is in the serious wear state from the beginning, and the wear of running-in phase is inflected by the work velocity and the state condition of the surface of the samples. The wear process which the mean value is a constant and the standard deviation is different is a normal process generally, it is a stationary normal process if the standard deviation has no relation to the start of the wear time, or a Wiener process if the standard deviation is liner with the wear time, it is valuable to forecast the wear reliability.