Microstructural evolution of Mn-based maraging steels and their influences on mechanical properties

The microstructural evolution in a set of Mn-based maraging steels (7–12 wt% Mn) when aged at 460–500 ºC for various durations up to 10,080 min and the influences on mechanical properties are systematically investigated. The improved yield strength of peak-aged samples is attributed to the formation of Ni2TiAl precipitates and the precipitation strengthening is governed by Orowan mechanism. Segregation of Mn at grain boundaries in the initial aging stage resulted in severe intergranular brittleness. During further aging, accumulated Mn segregation leading to the formation of ductile lath-like reverted austenite removed the embrittlement and significantly improved the ductility. In the overaged condition, the steady work hardening after yielding compensates the loss of yield strength resulting from the coarsening of precipitates and softening of α′-martensite matrix. There was only limited evidence of the TRIP effect in the reverted austenite, indicating that work hardening was associated with other deformation mechanisms. Increasing the aging temperature or the Mn content of alloy that promotes austenite reversion was demonstrated to accelerate the improvement of ductility

On the use of cryomilling and spark plasma sintering to achieve high strength in a magnesium alloy

Bulk nanostructured magnesium alloy AZ31 has been produced by spark plasma sintering at four different temperatures from 350 to 450 °C. The effect of sintering temperature on microstructural evolution and compression behaviour was studied in detail. It was concluded that the sample consolidated at 400 °C exhibited the highest strength. Higher sintering temperature (450 °C) improved the compressive strain of the bulk sample but at the sacrifice of strength. However, samples consolidated at 350 °C displayed brittle behaviour with low strength. All consolidated samples had a bimodal microstructure with nanocrystalline and coarse grains. The nanocrystalline microstructure formed by cryomilling was retained after consolidation and a maximum microhardness was approximately 150 HV. The bulk samples consolidated at 400 °C with an average grain size of 45 nm showed exceptional average true compressive yield strength of 400.7 MPa, true ultimate compressive strength of 499.7 MPa, which was superior to published results for most of conventional magnesium alloys. Although nanostructured materials usually have high strength but poor ductility, the material in this study exhibited high strength and a true compressive strain of 0.036

Microstructural evolution and wear mechanism of Ti3AlC2 – Ti2AlC dual MAX phase composite consolidated by spark plasma sintering (SPS)

In this work, we report the synthesis, deformation and tribological behaviour of a novel Ti3AlC2 – Ti2AlC MAX phase composite metallo-ceramic. The dual MAX phase composite was synthesized by spark plasma sintering (SPS) under a vacuum environment using Ti, Al, and C precursor powders. The deformation mechanism and the tribological behaviour were studied and analyzed by SEM, TEM, and Raman spectroscopy. The transition in friction and wear as well as the operative wear mechanisms involved were further discussed. Detailed analyses of the worn surface showed that Ti3AlC2 – Ti2AlC dual MAX phase composite is intrinsically self-lubricating

Proton-proton scattering above 3 GeV/c

A large set of data on proton-proton differential cross sections, analyzing powers and the double polarization parameter A_NN is analyzed employing the Regge formalism. We find that the data available at proton beam momenta from 3 GeV/c to 50 GeV/c exhibit features that are very well in line with the general characteristics of Regge phenomenology and can be described with a model that includes the rho, omega, f_2, and a_2 trajectories and single Pomeron exchange. Additional data, specifically for spin-dependent observables at forward angles, would be very helpful for testing and refining our Regge model.Comment: 16 pages, 19 figures; revised version accepted for publication in EPJ

The lubricating properties of spark plasma sintered (SPS) Ti3SiC2 MAX phase compound and composite

MAX phase composites Ti3SiC2–TiCx and Ti3SiC2–(TiCx + TiC) were synthesized and consolidated via a powder metallurgy spark plasma sintering (SPS) technique. The bulk compositions and microstructural evolution of the resulting SPS discs were analyzed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM) paired with an energy-dispersive spectroscopy (EDS) system. The tribological behavior of the synthesized discs was investigated at room temperature under dry sliding conditions using an Al2O3 ball by employing a ball-on-disc tribometer configuration. Postmortem analyses of the worn surfaces showed that the Ti3SiC2 MAX phase exhibited intrinsic self-lubricating behavior due to the evolution of easily sheared graphitic carbon at the sliding surface. The addition of stoichiometric TiC delayed the oxidation kinetics of Ti3SiC2, which favors the evolution of graphitic carbon in lieu of rutile and oxycarbide films. Thus, this work shows comprehensively the existence of an intrinsic self-lubricating behavior of Ti3SiC2 and the important role of secondary-phase TiC in the Ti3SiC2 matrix in its tribological behavior. The wear mechanisms in both composites are dominated by tribo-oxidation triggered by frictional heating. This is then followed by deformation-induced wear upon friction transition

An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics

For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types

Enhancing ductility and strength of nanostructured Mg alloy by in-situ powder casting during spark plasma sintering

Due to internal processing defects, bulk nanostructured Mg alloys have high strength but extremely poor ductility. A novel and facile process was designed and in-situ powder casting was initiated during spark plasma sintering. This process significantly reduced processing induced defects, enhanced inter-particle bonding and introduced significant precipitation without extra ageing treatment, leading to improvement of the compressive strength and ductility. The compressive strain of bulk sample consisting of pure cryomilled powder was 3.6% with an ultimate strength of 500 MPa, while cryomilled powder mixed with eutectic Mg-Zn alloy powder obtained a compressive strain of 6.6% and ultimate strength of 506 MPa. The ductility of the sample with mixed powder was increased by 83% without any sacrifice of strength compared to the sample consisting of only pure cryomilled powder

Ramification of thermal expansion mismatch and phase transformation in TiC-particulate/SiC-matrix ceramic composite

This article presents a microstructural study on the role of incipient residual stress relaxation in TiC-particulate/SiC-matrix ceramic composite toughened by thermal expansion mismatch and phase transformation toughening. Exhaustive microstructural studies was undertaken using scanning electron microscopy and transmission electron microscopy following a wear test. It was found that the superposition of hydrostatic tensile stress induced at the surface following the sliding contact on the inherent residual stresses locked in the composite led to a relaxation and/or reduction in the residual stresses. Stress relaxation presented a wider implication for the tribological properties of this ceramic matrix composite (CMC) in the form of a grain-scale rippling microstructural phenomena

Phase stability of a standing-wave free-electron laser

The standing-wave free-electron laser (FEL) differs from a conventional linear-wiggler microwave FEL in using irises along the wiggler to form a series of standing-wave cavities and in reaccelerating the beam between cavities to maintain the average energy. The device has been proposed for use in a two-beam accelerator because microwave power can be extracted more effectively than from a traveling-wave FEL. A simplified numerical simulation indicates that, with appropriate prebunching, the standing-wave FEL can produce an output signal that is effectively the same in all cavities. However, changes in the beam energy of less than 1% are found to introduce unacceptably large fluctuations of signal phase along the device. Analytic calculations and single-particle simulations are used here to show that the phase fluctuations result from beam synchrotron motion in the initial signal field, and an approximate analytic expression for the signal phase is derived. Numerical simulations are used to illustrate the dependence of phase fluctuations on the beam prebunching, the beam-current axial profile, and the initial signal amplitude