Microstructural stability and lattice misfit characterization of nimonic 263

Nimonic 263 has been selected as a candidate header/piping material of advanced ultra-supercritical (A-USC) boilers for the next generation of fossil fuel power plant. Experimental assessments on the microstructural stability of this material are presented in this paper. Microstructural evolution has been quantified by high resolution field emission SEM and TEM. Electron diffraction and the combined XRD and Gaussian peak-fitting have been applied to investigate the coherency and lattice misfit between the gamma prime precipitates and the gamma matrix. The microstructure subjected to solution and hardening treatment consists of gamma-matrix and a network of carbide precipitates along the grain boundaries. Large quantities of fine gamma prime-Ni3(Ti,Al) precipitates were observed, with an average size of 17 nm and coherent with the matrix lattice. The overall misfit has been quantified to be 0.28%. After long term aging at 700 and 725 °C for various periods up to 20,000 hours, gamma prime was still the predominant precipitate and mostly coherent with the matrix. A few needle-shape eta-Ni3Ti intermetallic precipitates were found in the grain boundary regions. The gamma prime size has grown progressively to 78 nm, accompanied by the gamma-gamma prime constrained misfit increasing to 0.50%. Moreover, the M23C6-type grain boundary carbides were found to have experienced morphological evolution, including the nucleation of Widmanstatten-type needles and their initial growth towards the matrix

Influence of power pulse parameters on the microstructure and properties of the AlCrN coatings by a modulated pulsed power magnetron sputtering

In this study, AlCrN coatings were deposited using modulated pulsed power magnetron sputtering (MPPMS) with different power pulse parameters by varying modulated pulsed power (MPP) charge voltages (350 to 550 V). The influence of power pulse parameters on the microstructure, mechanical properties and thermal stability of the coatings was investigated. The results indicated that all the AlCrN coatings exhibited a dense columnar microstructure. Higher charge voltage could facilitate a denser coating microstructure. As the charge voltage increased up to 450 V or higher, the microvoids along the column boundaries disappeared and the coatings became fully dense. The main phase in the AlCrN coatings was the c-(Al, Cr)N solid solution phase with NaCl-type phase structure. A diffraction peak of the h-AlN phase was detected at a 2θ of around 33°, when the charge voltage was higher than 500 V. The hardness of the AlCrN coatings varied as a function of charge voltage. The maximum value of the hardness (30.8 GPa) was obtained at 450 V. All the coatings showed good thermal stability and maintained their structure and mechanical properties unchanged up to 800 °C during vacuum annealing. However, further increasing the annealing temperature to 1000 °C resulted in apparent change in the microstructure and decrease in the hardness. The charge voltages also showed a significant influence on the high-temperature tribological behavior of the coatings. The coating deposited at the charge voltage of 550 V exhibited excellent tribological properties with a low friction coefficient

Effect of Deformation Rate on the Elastic-Plastic Deformation Behavior of GH3625 Alloy

GH3625 alloy is a typical polycrystalline material. The mechanical properties of a crystal within the alloy depend on the single crystal properties, lattice orientation, and orientations of neighboring crystals. However, accurate determination of single crystal properties is critical in developing a quantitative understanding of the micromechanical behavior of GH3625. In this study, the effect of deformation rate on the elastoplastic deformation behavior of GH3625 was investigated using in situ neutron diffraction room-temperature compression experiments, EBSD, and TEM. The results showed that the microscopic stress-strain curve included elastic deformation (applied stress σ ≤ 300 MPa), elastoplastic transition (300 MPa σ ≤ 350 MPa), and plastic deformation (σ > 350 MPa) stages, which agreed with the mesoscopic lattice strain behavior. Meanwhile, the deformation rate was closely related to the crystal elastic and plastic anisotropy. The results of the lattice strain, peak width, and peak intensity reflected by the specific hkl showed that the deformation rate had little effect on the elastic anisotropy of the crystal, but had a significant effect on the plastic anisotropy of the crystal. With the increase in the deformation rate, the high angle grain boundaries gradually changed to the low angle grain boundaries, and the proportion of twin boundaries gradually reduced. Also, the grains transformed from uniform deformation to nonuniform deformation. Moreover, with the increase in deformation rate, the total dislocation density (ρ) of the alloy first decreased and then increased, whereas the geometrically necessary dislocation density (ρGND) monotonically increased, and the statistically stored dislocation (SSD) density (ρSSD) monotonically decreased. Meanwhile, the abnormal work hardening behavior of the sample at a deformation rate of 0.2 mm/min was mainly related to the SSD generated by uniform deformation. Additionally, the contribution of dislocation strengthening and TEM observation confirmed that the dominant deformation of GH3625 was dislocation slip, and its work hardening mechanism was dislocation strengthening

Effect of Deformation Rate on the Elastic-Plastic Deformation Behavior of GH3625 Alloy

GH3625 alloy is a typical polycrystalline material. The mechanical properties of a crystal within the alloy depend on the single crystal properties, lattice orientation, and orientations of neighboring crystals. However, accurate determination of single crystal properties is critical in developing a quantitative understanding of the micromechanical behavior of GH3625. In this study, the effect of deformation rate on the elastoplastic deformation behavior of GH3625 was investigated using in situ neutron diffraction room-temperature compression experiments, EBSD, and TEM. The results showed that the microscopic stress–strain curve included elastic deformation (applied stress, σ ≤ 300 MPa), elastoplastic transition (300 MPa 350 MPa) stages, which agreed with the mesoscopic lattice strain behavior. Meanwhile, the deformation rate was closely related to the crystal elastic and plastic anisotropy. The results of the lattice strain, peak width, and intensity reflected by the specific hkl showed that the deformation rate had little effect on the elastic anisotropy of the crystal, but had a significant effect on the plastic anisotropy of the crystal. With the increase in the deformation rate, the high angle grain boundaries gradually changed to the low angle grain boundaries, and the proportion of twin boundaries gradually reduced. Also, the grains transformed from uniform deformation to nonuniform deformation. Moreover, with the increase in deformation rate, the total dislocation density (ρ) of the alloy first decreased and then increased, whereas the geometrically necessary dislocation density (ρGND) monotonically increased, and the statistically stored dislocation (SSD) density (ρSSD) monotonically decreased. Meanwhile, the abnormal work hardening behavior of the sample at a deformation rate of 0.2 mm/min was mainly related to the SSD generated by uniform deformation. Additionally, the contribution of dislocation strengthening and TEM observation confirmed that the dominant deformation of GH3625 was dislocation slip, and its work hardening mechanism was dislocation strengthening

Microstructure and arc erosion behavior of WC/CuCr30 composites based on nano-Cr precipitation

CuCr alloys with high contact performance for medium and high voltage vacuum circuit breakers are becoming increasingly urgent. In this work, WC/CuCr30 composites were prepared by SPS process, and nanometer-sized precipitated Cr phases were obtained by subsequent heat treatment. The microstructure and arc erosion behavior were investigated. The results show that nano-Cr phase precipitated in copper matrix can effectively improve the interfacial bonding strength between the Cu matrix and WC particles, and part of the precipitated nano-Cr phase is combined with the C element in WC to form nano-Cr23C6. Both nanophases can improve the resistance to dislocation and sub-grain boundary movement in the deformation process of WC/CuCr30 composite, thus improving the hardness of the copper matrix with a slight decrease in electrical conductivity. The results of electrical contact show that the addition of WC particles and nano-Cr precipitates can not only extend contact life of CuCr material, but also help to disperse the arc to avoid concentrated erosion. The presence of Cr23C6 phase around WC particles effectively improves the interfacial bonding between Cu phase and WC phase and reduces the probability of pore existence at the interface, which is beneficial to vacuum breaking performance

Sliding wear of medium-carbon bainitic/martensitic/austenitic steel treated by short-term low-temperature austempering

A medium-carbon Si–Mn–Ni–Cr–Mo alloyed (300M) steel was austempered for various short periods at its martensite-starting temperature of 285 °C to seek improved sliding wear resistance as compared to the traditional martensitic and bainitic steels. Reciprocating sliding wear tests were performed against a WC/Co ball counterpart at a constant load of 49 N. The samples were characterised using field emission SEM, XRD and hardness testing. The associated wear mechanisms were analysed using SEM and cross-sectional TEM. The results revealed that a short austempering time of 6 min produced refined arrays of initial nano-bainitic ferrite laths and inter-lath filmy austenite and the majority martensite and retained austenite, while the majority of the microstructure remained martensitic with retained austenite. The hardness was unchanged to that of the as-quenched martensite of 6.4 GPa. Simultaneously the wear coefficient decreased by 41% from 2.67 to 1.58 × 10-15 m3N-1m-1, which is also superior to both the tempered martensite at 1.65 × 10-15 m3N-1m-1 and the lower bainite at 1.87 × 10-15 m3N-1m-1. Increasing the austempering time to 20 and 60 min resulted in wear coefficients of 1.38 and 2.18 × 10-15 m3N-1m-1, respectively. The improved wear resistance has been explained by the wear induced microstructure evolution, especially the carbon partitioning induced stabilisation of retained austenite. The high-stress sliding wear was found to be dominated by severe shear deformation, which resulted in a nano-laminate structured top layer. Delamination wear was found to take place within the embrittled nano-laminates

Silibinin Causes Apoptosis and Cell Cycle Arrest in Some Human Pancreatic Cancer Cells

Silibinin, an effective anti-cancer and chemopreventive agent in various epithelial cancer models, has been reported to inhibit cancer cell growth through mitogenic signaling pathways. However, whether it can inhibit human pancreatic carcinoma growth and what are the underlying mechanisms is still not well elucidated. Here, we evaluated the inhibitory proliferation effects of Silibinin in pancreatic carcinoma growth and examined whether Silibinin modulates cell cycle and apoptosis. Our results indicate that Silibinin effectively inhibited the pancreatic carcinoma AsPC-1, BxPC-3 and Panc-1 cells’ proliferation and caused apoptosis. Silibinin induced a decrease in S phase and cell cycle arrest in G1 phase in AsPC-1 cells, but had no obvious changes in BxPC-3 and Panc-1 cell cycle. Furthermore, these results suggest that Silibinin might be a candidate chemopreventive agent for pancreatic carcinoma therapy

Enhanced plastic deformation ability of copper matrix composites through synergistic strengthening of nano-Al2O3 and Cr particles

The commercial application of Al2O3/Cu composites (ODS copper) with high Al2O3 content is consistently restricted by their plastic deformability. In order to synergistically improve the plastic deformability of Al2O3/Cu composites, Al2O3/Cu–Cr composites with different Cr contents are prepared by internal oxidation combined with heat treatment by replacing part of the Al2O3 particles with Cr phases heat treatment. The effects of Cr content on the microstructure and plastic deformability of Al2O3/Cu–Cr composites are investigated. It is found that the nano-Al2O3 (8 nm) and Cr (25 nm) particles are uniformly distributed in the copper matrix, and both reach a semi-congruent interface with copper matrix. Meanwhile, the copper matrix undergoes a transition from a [111]Cu hard orientation to a [100]Cu soft orientation, and the increase in Cr content leads to a more pronounced degree of recrystallization in the Al2O3/Cu–Cr composites. The results of geometric phase analysis (GPA) show that the coordinated deformability between Cr and Cu is better than that between Al2O3 and Cu. The elongation of 2.5Al2O3/Cu-0.3Cr composite increased to 24.48 % from 22.47 % of the Cr-free 2.8Al2O3/Cu composite. The results of tensile strength calculations show that the tensile strength of Al2O3/Cu–Cr composites is mainly dominated by matrix strengthening and Orowan strengthening induced by Al2O3 particles, while grain strengthening, dislocation strengthening, and Orowan strengthening induced by Cr particles play a secondary role. The correlation coefficient (R2) is 0.95 after fitting the experimental and theoretical values of tensile strength of Al2O3/Cu–Cr composites

Tribological properties and wear mechanisms of DC pulse plasma nitrided austenitic stainless steel in dry reciprocating sliding tests

Expanded austenite (Gamma-N), or S-phase, is a special phase of low-temperature nitrided austenite containing highly super-saturated nitrogen in the form of heterogeneous Cr-N nano-clusters. A nitrided layer of singe phase N is known to provide austenitic stainless steel with combined high hardness, good wear resistance and superior corrosion resistance. This paper reports recent experiments on a comparative study of the sliding wear properties and wear mechanisms of nitrided austenite stainless steel AISI 316, with a special attention paid on worn surface structural evolutions induced by frictional heating and sliding deformation. The samples were prepared by DC pulsed plasma nitriding treatments of various time at a fixed power. Knoop micro-indentation has revealed hardening behaviour of the nitrided samples. The reciprocating ball-on-disc sliding wear and friction properties were investigated at ambient environment conditions using an alumina counterpart ball. The worn surfaces have been analysed by XRD,FEG-SEM and EDX to show wear induced changes in the crystalline characteristics and the wear mechanisms of tribo-oxidation, cracking, abrasive wear and ploughing deformation. Moreover, longitudinal cross-sectional foils of the worn samples have been prepared and analysed using TEM, to investigate the wear induced structural changes, including tribofilm formation, plastic deformation and delamination in depths of nano-scale