Advanced Materials Research Vols. 146-147

Abstract: Due to the limitations of the existing strength theories or criteria, the phenomenon of material failure cannot be not fully explained, which makes material strength criterion to always be an important direction to study. Reference [1] found that there was a certain relationship between elastic strain and plastic strain, and a preliminary summing-up of this relationship had been done.Based on the relationship, the dominant factor of material failure has been analyzed, and a new strength criterion has been established with plastic strain as the control value. The new criterion is of simple expression, and can be used to explain very well some experiment phenomena.

Abstract: The mechanism responsible for the formation of recrystallization texture is still disputed although recrystallization texture has long been a subject of research. This is mainly related to the complexity of recrystallization itself .The mechanism of recrystallization microtexture Cold-rolling low carbon sheet steel based on CSP was investigated by the electron back scatter diffraction(EBSD) was investigated. In addition, the origin of nuclei with specific orientations was studied. The results showed that the formation of recrystallization texture is explained by oriented nucleation and the nucleis show around 50% frequency of 15–60°misorientation with their surrounding deformed matrices. Deformed γ-fibre texture components increase more rapidly during the early stage of recrystallization. In contrast, the deformed α-fibre components, such as {001}<110> components disappear rather rapidly early stage of recrystallization and {112}<110> components increases rapidly late stage of recrystallization and grains growth. By microcosmic orientation distribution analyse find that the new {011}<100> grains are nucleated within shear bands in the deformed {111}<112> grains, New {111}<112> grains are nucleated within deformed {111}<110> grains and new {111}<110> grains originated in the deformed {111}<112> grains .

Abstract: The crack tip region in an elastic composite can be separated into three different regions. based on a simple rate-independent phenomenological constitutive model, the path independence of the J-integral and the concept of cracktip shielding, the maximum radii R of the damage saturation zone is obtained. Damage isotropy in the largest saturated damage zone is expressed by utilizing the Monte-Carlo technique to create the uniform distributions of microcrack location and orientation. With the assumption of dilute microcrack concentration, interaction among microcracks are neglected, and the stress intensity factor produced by interaction between main-crack and each microcrack can be superposed. Two sources of loading are analyzed, one is for the main-crack microcrack interaction under an applied remote load, and the other is for the main-crack microcrack interaction accompanied by the relief of residual stresses on the microcrack surfaces. The results show that two sources of loading can shield the main-crack tip, and microcracks behind the main-crack tip can make the most shielding whereas microcracks ahead of the main-crack tip play no role in shielding.

Abstract: Fatigue crack propagation tests in the Paris region were performed in order to get compressive loading effect on fatigue crack growth at negative stress ratio (R) in 2A12 aluminum alloy. The results of the tests showed that the effect of the compressive loading part of the applied stress cycle on fatigue crack growth rate da/dN in 2A12 aluminum alloy at negative stress ratio can not be omitted. The fatigue crack growth rate at R<0 was more than that at R>0 under the same range of stress intensity factor Kmax. The da/dN is the function of Kmax and stress ratio R. The promoting effect has an increase trend with the increase of the absolute value of the negative stress ratio R. Then a model involved compressive loading effect on fatigue crack propagation at negative stress was obtained. The model has been obtained good agreements with the experimental data.

Abstract: The behaviors of precipitation and recrystallization aging at 900 after cold work in a Fe-18Cr-12Mn-0.48N high-nitrogen austenitic stainless steel were investigated by means of optical microscopy (OM) and transmission electron microscopy (TEM). The results show that precipitation and recrystallization occur simultaneously after aging at 900 for 10min. The precipitates firstly appear at dislocation, sub-boundary and inside the subgrain. Precipitation at these positions hinders the formation of recrystallization nucleus. With aging time increasing, precipitates appear in the recrystallized grain boundary and inside the grain. Precipitation at these positions hinders the growth of the recrystalized grains.

Abstract: As a professional with strong theoretical and practical in a new college, the guidance major-materials science and engineering involves extremely broad field. Our reform ideas and practices are only to training science-based applied talents possessing engineering capabilities. Facing the new situation on the demand for materials engineering personnel, we reform curriculum and teaching to get rid of the drawbacks of the original content and build the professional training program with the characteristics and course system.

Abstract: The characteristics of different types of the weighted functions are discussed, and the dependency of the influence domain on the intrinsic length scale is examined. Distribution of stress field of I-II mixed mode crack is analyzed by non-local theory with different types of weighted functions. The effects of the stress intensity factor KI and KII on the all components of strains at the crack tip are analyzed by the non-local theories based on different types of weighted functions. The non-local strain will be considerably reduced. The size of non-local strain field with the bell-shaped weighted functions is larger than that obtained by either Green’s or Gaussian weighted functions. The non-local theory is instructive to avoid the trouble resulting from stress singularity at crack tip.

Abstract: The structure evolutions of Al83Ni10Ce5Si2, Al83Ni10Ce7, Al85Ni10Ce5, Al87Ni7Nd6 and Al87Ni5Co2Nd6 metallic glasses have been studied in detail. The studies establish a relation between the amount of medium range order (MRO) and crystallization mode. An increased amount of MRO suppresses the precipitation of primary fcc-Al and transforms the crystallization mode from a primary crystallization (Al87Ni7Nd6) to a eutectic crystallization (Al87Ni5Co2Nd6); while a decreasing amount of MRO promotes the precipitation of primary fcc-Al and transforms the crystallization mode from a eutectic crystallization (Al83Ni10Ce7 and Al85Ni10Ce5) to a primary crystallization (Al83Ni10Ce5Si2).

Abstract: In this paper, we made two different chemical conversion coatings on aluminum alloy by TiOSO4 and Na2WO4. The morphology of the chemical conversion surface layers were observed by scanning electron microscopy (SEM). The microcosmic phase structures were characterized using X-ray diffraction (XRD). Electrochemical method was used to study the coatings corrosion resistance. The results indicated that the two conversion coatings were crystal structure material, the surface of coating were both show pothole structure. TiOSO4 coating have better corrosion resistance than Na2WO4 coating.

Abstract: The getters composed with Titanium and Zr-V-Fe were prepared by conventional powder metallurgical technology. The sorption properties and mechanical strength of the Ti-Zr-V-Fe getter prepared with three different average particle sizes of Titanium powder were investigated. The results showed that the smaller Titanium powders particle size can effectively improve the property of the nonevoparobal getter, but if particle size is too small, the sorption of the getter will decrease. The getter which was added with Titanium powder of 48μm has the best hydrogen sorption capability. With the decrease of the size of Titanium powder, mechanical strength will be improved remarkably. In the paper, the sorption characteristics for different gases were analyzed initially and the understanding for Zr-based getter is more extensive. The results show that the getters can adsorb activated gases, such as H2, N2 and CO. The pumping speed for H2 is best than that for N2 and CO.