Materials Science Forum Vol. 879

Abstract: Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials’ mechanical and surface properties in different types of components, mostly as a means of enhancement of their fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists in the generation of relatively deep compression residual stresses fields into metallic components allowing an improved mechanical behaviour. In this paper, the special case of Ti6Al4V alloy is considered from a more fundamental point of view, with specific consideration of the microstructural changes and residual stresses fields justifying those macroscopic effects. From a concrete point of view, the effect of the application of different typical LSP intensities on the microstructure and residual stresses fields introduced in this material and their possible correlation to the associated surface effects are analyzed.

Abstract: The deformation microstructures and mechanical properties of an austenitic stainless steel subjected to warm plate rolling were studied. The warm rolling was carried out at 300°C to different total true strains of 0.5, 1, 2 or 3. The structural changes during warm rolling were characterized by the elongation of original grains towards the rolling direction and the development of spatial network of strain-induced high-angle boundaries leading to the evolution of ultrafine-grained microstructure at sufficiently large strains. The grain refinement was assisted by the development of deformation twinning. After straining to 3, the transverse grain size decreased down to 220 nm in the warm rolled samples. The warm plate rolling resulted in significant strengthening. The microhardness increased from 2910 MPa to 4192 MPa with increase in the total strain from 0.5 to 3. Correspondingly, the yield strength approached 1005 MPa after warm rolling to a total strain of 3.

Abstract: Q&P annealing cycles with different partitioning conditions were performed on cold rolled 0.2C-2.22Mn-1.44Si-0.21Cr steel. An important influence of partitioning temperature and time on the evolution of retained austenite fraction was shown through the saturation magnetization measurements. Such effect of partitioning conditions was also observed on the evolution of mechanical behavior. The evolution of microstructure and mechanical properties with the partitioning conditions was analyzed. Mechanical stability of retained austenite as a function of partitioning time was also assessed. Finally, modeling of the obtained stress-strain curves was performed and some explanations of the observed tendencies between partitioning conditions and tensile properties were proposed.

Abstract: The authors have developed the texture measurement system at iMATERIA, which is the neutron diffractometers built in Materials and Life Science Experimental Facility (MLF) at J-PARC, Japan. The high flux of the incident beam and Time-Of-Flight method enabled the complete texture measurement within several minutes in case of steels. Since the neutron beam can transmit most of the materials, the measured texture represents the state of whole exposed volume. The multi-histogram analysis also enables to determine phase fractions in a multiphase material as well as the texture of each phase.

Abstract: The thermodynamic modeling of alloy systems consisting of stable and metastable phases e.g. high-alloyed mottled cast iron can be problematic. Thermodynamic databases are rather well-developed for low, medium and high alloyed steels (e.g. HSS) but the application of those databases is not yet very common for high-alloyed (mottled) cast irons. The Thermo-Calc software together with the TCFE7 database is used to calculate isopleth and property diagrams, using the CALPHAD method. Additionally Scheil-Gulliver calculations are performed to simulate the effects of microsegregation during solidification. The results from the thermodynamic calculations are compared with measurements on own samples and with literature values. Those measurements include quantitative light-optical analysis, SEM with BSE detector, EDX measurements for the distribution of the alloying elements as well as XRD and DSC measurements. The investigations show the possibilities which are offered by thermodynamic calculations for high-alloyed mottled cast iron as well as the limitations and the compromises which have to be taken into account when calculating stable and metastable phases existing next to each other.

Abstract: Multipass friction stir processing (FSP) technique was used to get inhomogeneous layered microstructure in Al 5086 alloy. Different proportions of fine and coarse grain microstructures were generated using FSP. In the present work, material with inhomogeneous layered microstructure generated using FSP was subjected to deformation at temperature of 500°C and at strain rate in the range of 5×10^-4 to 1×10^-2 s^-1. It was observed that the inhomogeneous layered microstructure with more than 50% fine grain microstructure is required to get higher elongation to failure. However material having homogeneous fine grain microstructure showed lower elongation to failure than the material having both fine and coarse grain microstructures. By varying the proportion of fine and coarse grain microstructures higher ductility was obtained at higher strain rate as compared to a material with homogeneous microstructure. It is clear that materials with inhomogeneous microstructure are not following “rule of mixture” type of behaviour.

Abstract: In the present work, critical testing methods are employed in order to assess the formability of a Zn-Ti-Cu alloy, evaluating, therefore, the anisotropic properties of the produced sheet. The determination of plastic strain ratios and the induced combined mathematical expressions, utilizing bi-axial strain measurements for the various test directions (0, 45 and 90 degrees towards the RD), together with the performance of cupping tests are compiled, aiming to rank and interpret the bending and sheet metal roll-forming capability. Moreover, the microstructural characterization is realized to address the influence of grain and phase structure on the sheet metal formability and identify potential optimization routes. Fracture analysis approach elucidated the micro-mechanisms prevailed in damage evolution and accumulation during monotonic loading, signifying the importance of microstructure development during thermomechanical process history.

Abstract: In order to understand the effects of the solute element and its concentration on the formation of texture, uniaxial compression tests were carried out at various deformation conditions with different aluminum solute concentration in rolled AZ magnesium alloy (AZ31, AZ61, AZ91). To clarify the texture measurements and crystal orientation distribution, X-ray diffraction methods were conducted on mid plane section of the specimens. As a result in this study, the formation of fiber texture and occurrence of dynamic recrystallization were observed in all case of specimens. The main components and its sharpness of texture were varied depending on deformation conditions and Al concentrations. Especially, accumulation of basal texture was developed with an increasing of Al concentration.

Abstract: Two important objectives of the automotive industry are the decrease of the body-in-white weight and the improvement of the passenger safety. High strength steels (HSS) are widely used to achieve these objectives. Quenching and partitioning (Q&P) has recently been proposed to achieve high strength steel grades for the third generation of advanced high strength steels (AHSS), which contain a considerable amount of retained austenite. Due to their microstructure these new steel grades combine a high tensile strength with good elongation values, as long as cementite precipitation is avoided. A model describing the involved phase transformations is presented. Special focus is put on the cementite precipitation and how it is influenced by silicon and aluminum additions.

Abstract: To improve the weld quality of AA 5083 plate using AA 5356 filler rod, an automatic TIG welding system is developed, by which welding speed can be controlled and a uniform speed is obtained. Welding of aluminium 5083 plate is carried out for different welding currents and welding speeds. In this work, the effect of welding speed and current on, the tensile strength of the weld, hardness at the three different zones viz. weld metal, HAZ and base metal are investigated. The temperature is measured at the HAZ and base metal. The hardness and temperature on the weld zone and the base metal are greatly influenced by the welding speed and current. It is found that the weld strength is influenced by different values of weld current and speed, but sometimes with high current, welding speed has no specific effect on the tensile strength of the weld. The effect of material deposition rate on the weld strength in uniform welding is studied. The weld thickness to width ratio is an important aspect in the analysis of weld strength. The values obtained for current and speed are taken for optimizing the strength and hardness, using Taguchi method and utility concept.