The efficiency of Cu(In,Ga)Se2 (CIGS)-based solar cells could be continuously increased up to 22.6% by employing alkali metal dopants like Na, K, Rb, and Cs. The alkali metals are supplied to the CIGS layer from the glass substrate during deposition, from precursor layers or by a post deposition treatment. The alkali metal distribution in CIGS is not homogenous. Independently of the alkali metals used, their concentration at grain boundaries is much higher than that inside the grains. In this contribution, we discuss thermodynamic limitations for alkali metals in CIGS and show that in higher concentrations they are responsible for secondary phase separation. Applying the concept of immiscibility of phases for alkali metals in CIGS, we suggest how segregation at grain boundaries, formation of clusters in CIGS grains, sporadic formation of microstructures in the CIGS layer (hotspots, nodules), and separation of secondary phases with ordered structures can be interpreted.

The codeposition characteristics of Si–B–N ceramics from the SiCl4–NH3–BCl3–H2–Ar system at lower temperatures and phase transformation of as-prepared Si–B–N ceramics at temperatures from 1200 to 1800 °C were investigated. Thermodynamic analysis results indicated that the BN + Si3N4 dual phase region existed from 800 to 1200 °C and that 800 °C was an optimum deposition temperature to deposit Si–B–N ceramic coating. Deposition efficiencies at equilibrium for Si3N4 and BN were high, particularly at temperatures below 1000 °C. Pressure and dilution ratio of H2 had little influence on deposition efficiencies of BN and Si3N4 at 800 °C. The amorphous Si–B–N ceramic coatings were successfully deposited at 800 °C from the same precursor system and contained N–B and N–Si bonds by XPS analysis. It kept amorphous below 1600 °C in N2 and partly transformed to α/β-Si3N4 when heat treated at 1600 °C in N2 for 2 h. These results demonstrated that the composite Si–B–N ceramics could be fabricated at 800 °C and used below 1600 °C.

Ti6Al4V alloys usually need to undergo some kind of surface treatment to enable good bone growth and implant integration. In this work, three treatments that modify the titanium alloy surface were studied with the aim of promoting osteogenic differentiation of human-embryonic-stem-cell-derived mesenchymal progenitors (hESC-MPs). The surface treatments used were mechanical polishing and electropolishing for 4 or 12 min in an H2SO4/HF/glycerine solution. The samples were characterised by atomic force microscopy, profilometry, X-ray photoelectron spectroscopy, and wettability. Samples were seeded with hESC-MPs in osteogenic media, and the cell number and alkaline phosphatase activity were measured. The electropolishing surface treatments influenced the nanometric morphology and wettability. However, the electropolished surfaces contributed in the same way as the mechanically polished surface to osteogenic differentiation, indicating that differentiation was strongly influenced by microroughness, which did not differ among the treatments used in the present work.

Many issues concerning the transformation behaviors in the Ni-rich Ti–Ni system remain unresolved, such as the isothermal nature of the B19′-martensitic and R-phase transformations and the precursor phenomena in the B2-parent phase. To clarify the origins of these behaviors, we investigated the transformation latent heat, specific heat, and superelastic behaviors of several Ni-rich Ti–Ni alloys in terms of the entropy change. An anomalous, very wide hump in the specific heat was detected for the B2-parent phase, which can likely be attributed to the precursor phenomenon in the B2-parent phase. In the critical region where the anomalous hump intersects the B19′-martensitic transformation, some evidences of the R-phase transformation were observed, such as a tweed-like microstructure and a specific heat peak with first-order-transformation characteristics. These findings suggest a strong relationship between the R phase and the precursor state in the B2-parent phase.

The predictability of modified constitutive model, based on Arrhenius type equation, for illustrating the flow behavior of Fe–36%Ni Invar alloy was investigated via isothermal hot compression tests. The hot deformation tests were carried out in a temperature range of 850–1100 °C and strain rates from 0.01 to 10 s−1. True stress-true strain curves exhibited the dependence of the flow stress on deformation temperatures and strain rates, which then described in Arrhenius-type equation by Zener–Holloman parameter. Moreover, the related material constants and hot deformation activation energy (Q) in the constitutive model were calculated by considering the effect of strain as independent function on them and employing sixth polynomial fitting. Subsequently, the performance of the modified constitutive equation was verified by correlation coefficient and average absolute relative error which were estimated in accordance with experimental and predicted data. The results showed that the modified constitutive equation possess reliable and stable ability to predict the hot flow behavior of studied material under different deformation conditions. Meanwhile, Zener–Holloman parameter map was established according to the modified constitutive equation and used to estimate the extent of dynamic recrystallization.

Age-hardening of homogenized and cold-rolled invar-based Sn alloys results in the development of continuously-formed (CP) and discontinuously-formed (DP) Ni3Sn2 precipitates. In situ investigation of the DP reaction front (RF) velocity (V) revealed a nonsteady-state behavior upon early aging stages followed by a constant V after prolonged aging. The reason for the initial nonsteady-state behavior was experimentally studied and attributed to the reduction of matrix Sn-supersaturation ahead of the DP RF as a result of the simultaneous CP coarsening (in homogenized specimen) or the CP increased volume fraction (in cold-rolled specimen). A similar trend of V variation in the homogenized specimen was obtained after the modification of the original Hornbogen model for the nonsteady-state DP growth kinetics. In general, variations of the transformed matrix fraction via the DP reaction suggest the faster kinetics of this reaction in cold-rolled specimen as compared to the homogenized one due to the existence of more nucleation sites induced by the cold deformation.

To investigate the solute transport and redistribution in the slab continuous casting processes of high sulfur steel, a three-dimensional model coupling turbulent flow, heat and solute transportation was developed. And then a thermodynamic model for MnS precipitation was established to study the MnS precipitation and distribution in strand on a macroscale and its effect on solute macrosegregation was also explored. The results showed that the temperature and solutes concentration were the main factors for the precipitation of MnS. The effect of temperature was significant when the solid fraction was greater than 0.8. Due to the precipitation of MnS, the segregation ratio of solutes Mn and S on the center line declined from 1.05–1.15 to 0.97–1.01 and from 1.2–1.45 to 1.00–1.08, respectively. And the solute concentration of Mn and S declined and distributed more uniformly in the strand, and the macrosegregation of Mn and S was also suppressed greatly.

Hot deformation behavior and microstructure evolution of as-cast Mn18Cr18N austenitic stainless steel were investigated by isothermal compression experiments. The results indicate that the microstructure evolution of the as-cast Mn18Cr18N steel is sensitive to strain rates. Discontinuous dynamic recrystallization, characterized by nucleation and growth controlled by grain boundary migration, occurs at lower strain rates. However, higher strain rates result in higher adiabatic temperature rise, which could be contributed to dynamic recrystallization (DRX) nucleation and growth by acceleration boundary migration. In addition, at higher strain rates, a large number of deformation microbands in the interior of coarse columnar grains were observed, which would provide potential nucleation sites for DRX. Meanwhile, a great number of Σ3 twins were observed, which reveals that twinning accelerates the separation of subgrains from bulging grain boundaries, and the iterative processing among Σ3 twins and its variants promotes the transformation from specific CSL grain boundaries to random high-angle boundaries.

A series of hot compression tests of medium carbon Cr–Ni–Mo-alloyed steel, 34CrNiMo steel, were conducted on a Gleeble-1500 thermal mechanical simulator, in a wide temperature range of 1173–1423 K and at a strain rate range of 0.002–5 s−1. Three constitutive models, namely the Johnson–Cook (JC) model, strain compensated Arrhenius model, and the physically based constitutive model, were established to describe the hot deformation of 34CrNiMo steel. A comparative study of the three models was investigated by comparing the accuracy of prediction of flow stress behavior. The results imply that the JC model is not able to adequately represent the high-temperature flow behavior with the existance of recovery and recrystallization. The Arrhenius-type model based on mathematics has a good prediction in the flow stress behavior in all strain ranges during the hot deformation. The physically based constitutive model gives a better prediction accuracy of the deformation behavior in both flow stress and deformation mechanism.

Ultrasonic vibration can lead to significant load reduction in metal forming, and this concept has been widely applied in microforming. Recently, we discovered that low-frequency mechanical vibration (less than 100 Hz) with micro-amplitudes also features the same effects. In this study, low-frequency vibration-assisted tensile deformation experiments were conducted on commercially low-carbon steel. Effects of vibration softening and residual softening were obtained during experiments. Both these softening effects became prominent at high vibration amplitudes. Detailed microstructural analyses reveal that a low-frequency vibration treatment altered the interior characteristics of the metal. Electron backscatter diffraction results showed low-angle grain boundaries, and the interior misorientation angle increased greatly with the application of a low-frequency vibration. Changes in the microstructure became more pronounced with the rise of vibration amplitudes. Instantaneous stress reduction results from the additional energy applied in the form of vibration, which lowers the barrier energy for the dislocation motion. The residual softening effect can be interpreted via a dislocation density decrease as a result of vibration markedly improving the opportunity for dislocation annihilation or stacking.

In the present work, the evolution of microstructure and mechanical properties of high-strength low-alloy D6AC steel containing the Ce element was synthetically investigated by means of electron backscatter diffraction, scanning electron microscope, Transmission electron microscope, and tensile and impact tests. The experimental results show that adding a certain amount of Ce into HSLA-D6AC steel can refine grains and martensite laths, as well as increase the fine VC precipitates, which not only enhance the strength of the steel but also improve the toughness and plasticity. Meanwhile, the morphology of martensite in HSLA-D6AC steel changes from twin martensite to dislocation martensite. It is found that after adding Ce, HSLA-D6AC steel exhibits a distinct necking stage in the tensile test, and the impact toughness value increases from 83 to 136 J. With the appearance of some more and deeper homogeneous dimples, the quasi-cleavage fracture transforms into a ductile fracture characterized by microvoid coalescence, demonstrating that HSLA-D6AC steel with the Ce element achieves excellent comprehensive mechanical properties.

Microstructure and pitting corrosion behavior of base metal (BM), heat-affected zone (HAZ), and weld zone (WZ) in the 316L stainless steel weld joint was investigated. The results indicated that WZ, including ferrite and austenite phases, was mainly composed of columnar dendrites, while BM and HAZ exhibited a full-austenite structure with low Σ coincidence site lattice boundaries especially twin boundary primarily. No obvious pitting occurred in WZ, while the millimeter-scale pits were observed in HAZ and BM after immersion test in 6% FeCl3 solution. HAZ had a lower pitting potential than WZ and BM, while not much difference in pitting potential was observed between WZ and BM. Dendrite-selected corrosion occurred in WZ, while grain boundary was the preferable site for pitting corrosion in HAZ and BM. Gain refinement and a decrease in twin boundary volume fraction promoted the pitting corrosion susceptible of HAZ.

Material mechanical behavior of tube has an essential influence on cross-sectional deformation of rectangular waveguide tube in rotary draw bending (RDB) process. Thus, taking widely used 3A21 aluminum alloy and H96 brass rectangular tubes as research objects, the cross-sectional deformation of these tubes in RDB with and without mandrel was investigated using the reliable three-dimensional finite element models. The results show that when no mandrel is used, compared with 3A21 tube, the position of wrinkle initiation for H96 tube is closer to the final bending section, and the cross-sectional deformation of H96 tube along bending direction is more homogeneous. When a mandrel is used, in bending process, the cross-sectional deformation of 3A21 tube in mandrel support zone (MSZ) is in coincidence with that of H96 tube, and the deformation of 3A21 tube is larger in transition zone (TZ) while smaller in no mandrel affect zone (NMAZ) than that of H96 tube. In retracting mandrel or springback process, the cross-sectional deformation of 3A21 tube in MSZ and TZ is constantly larger than that of H96 tube, while in NMAZ, the deformation of both tubes reverses.