Dual heterogeneous structures lead to ultrahigh strength and uniform ductility in a Co-Cr-Ni medium-entropy alloy

Alloys with ultra-high strength and sufficient ductility are highly desired for modern engineering applications but difficult to develop. Here we report that, by a careful controlling alloy composition, thermomechanical process, and microstructural feature, a Co-Cr-Ni-based medium-entropy alloy (MEA) with a dual heterogeneous structure of both matrix and precipitates can be designed to provide an ultra-high tensile strength of 2.2 GPa and uniform elongation of 13% at ambient temperature, properties that are much improved over their counterparts without the heterogeneous structure. Electron microscopy characterizations reveal that the dual heterogeneous structures are composed of a heterogeneous matrix with both coarse grains (10∼30 μm) and ultra-fine grains (0.5∼2 μm), together with heterogeneous L1₂-structured nanoprecipitates ranging from several to hundreds of nanometers. The heterogeneous L1₂ nanoprecipitates are fully coherent with the matrix, minimizing the elastic misfit strain of interfaces, relieving the stress concentration during deformation, and playing an active role in enhanced ductility.

Improving both strength and ductility simultaneously in structural metals and alloys remains a challenge. Here, the authors design a heterogeneous structure in a Co-Cr-Ni alloy that results in ultrahigh strength and significant uniform elongation.

Epidemiology and risk factors for chronic kidney disease in Chinese patients with biopsy-proven lupus nephritis

BACKGROUND

Lupus nephritis (LN) is one of the most serious complications of systemic lupus erythematosus (SLE). It is the most common secondary glomerulonephritis leading to end-stage renal disease.

AIM

The purpose of this study is to evaluate the epidemiology and risk factors of chronic kidney disease (CKD) in Chinese patients with LN.

METHODS

Clinical, laboratory, renal histopathology, treatment and outcome data were collected and retrospectively analysed in LN patients with or without CKD.

RESULTS

At the end of the study, 94 (45.63%) patients were identified as having CKD among 206 individuals with renal biopsy-proven LN. Renal function, represented by serum creatinine and estimated glomerular filtration rate, was significantly decreased in the CKD patients (P = 0.008 and P < 0.001, respectively) at the time of the kidney biopsy. Compared with the non-CKD group, significantly increased proportions of hypertension (P < 0.001), serositis (P = 0.042) and anti-histone antibody positivity (P = 0.004) were detected in the CKD patients. Renal pathological activity and chronicity index scores were significantly increased in the CKD group (P < 0.001 for all). Finally, hypertension (hazard ratio (HR) 2.432, 95% confidence interval (CI) 1.575-3.754, P < 0.001), anti-histone antibody (HR 2.907, 95% CI 1.837-4.600, P < 0.001), and tubular atrophy (HR 1.248, 95% CI 1.007-1.547, P = 0.043) were independent risk factors for CKD.

CONCLUSIONS

Hypertension, anti-histone antibody and tubular atrophy are independent risk factors for CKD in Chinese LN patients.

Low prevalence of hepatitis B virus infection in patients with autoimmune diseases in a Chinese patient population

Hepatitis B is a very common communicable disease in China but the prevalence of hepatitis B virus (HBV) infection in patients with autoimmune diseases is unknown. We retrospectively investigated the prevalence of autoimmune diseases in patients with HBV infection. The medical records of 4060 patients with autoimmune or nonautoimmune diseases were reviewed. A positive test result for hepatitis B surface antigen (HBsAg) was used to indicate the presence of HBV infection. Autoimmune diseases included autoimmune hepatitis, primary biliary cirrhosis, systemic lupus erythematosus and ulcerative colitis. Nonautoimmune conditions included inguinal hernia, appendicitis and pregnant or postpartum women. The proportion of autoimmune disease patients who were HBsAg positive (2.24%) was significantly lower than that of nonautoimmune disease patients who were HBsAg positive (4.58%; P = 0.0014). Regarding hepatic autoimmune diseases, the positivity rates for HBsAg in autoimmune hepatitis patients (0.83%) and primary biliary cirrhosis patients (1.02%) were both significantly lower than in nonautoimmune patients (4.58%; P = 0.006 and 0.004, respectively). Patients with hepatic autoimmune disease were significantly less likely to be HBsAg positive (0.93%) than patients with non-hepatic autoimmune disease (3.99%; P = 0.002). Patients with autoimmune diseases, especially those with hepatic autoimmune disease, may more efficiently clear HBV than patients with nonautoimmune diseases.

Deformation-induced structural transition in body-centred cubic molybdenum

Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama–Wassermann and Kurdjumov–Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.

Structural phase transitions are known to accommodate plastic deformation in some metals and ceramics. Here, the authors observe the in situ transformation of body-centred cubic molybdenum to face-centred cubic, and finally to body-centred cubic, allowing for 15.4% tensile strain accommodation.

Microstructural fingerprints of phase transitions in shock-loaded iron

The complex structural transformation in crystals under static pressure or shock loading has been a subject of long-standing interest to materials scientists and physicists. The polymorphic transformation is of particular importance for iron (Fe), due to its technological and sociological significance in the development of human civilization, as well as its prominent presence in the earth's core. The martensitic transformation α→ε (bcc→hcp) in iron under shock-loading, due to its reversible and transient nature, requires non-trivial detective work to uncover its occurrence. Here we reveal refined microstructural fingerprints, needle-like colonies and three sets of {112}<111> twins with a threefold symmetry, with tell-tale features that are indicative of two sequential martensitic transformations in the reversible α→ε phase transition, even though no ε is retained in the post-shock samples. The signature orientation relationships are consistent with previously-proposed transformation mechanisms, and the unique microstructural fingerprints enable a quantitative assessment of the volume fraction transformed.

Medium range order of bulk metallic glasses determined by variable resolution fluctuation electron microscopy

Variable resolution fluctuation electron microscopy (FEM) experiments are implemented with hollow-cone dark-field transmission electron microscopy. Medium range order lengths of zirconium and iron based bulk metallic glasses and amorphous silicon nitride are determined from the FEM results. It shows that maximum normalized intensity variances of FEM images occur when their nominal resolution approaches the correlation length Λ of the amorphous materials. Additionally, differences in the length and magnitude of medium range order are compared between metallic and covalent bond amorphous materials.

The role of estrogen and estrogen receptors in chemoresistance

Drug resistance is one of the major obstacles limiting the success of cancer chemotherapy. Biological mechanisms contributing to drug resistance may be present de novo and related to inherent features or may be raised after exposure to anticancer drugs. In recent years, both clinical observations and experimental studies suggested that steroid hormones and their receptors might also affect the therapeutic efficacy of antineoplastic drugs. Estrogens and estrogen receptors (ER) are well-known for their critical roles in the development and progression of breast tumors. It has long been known that breast tumors expressing ERα protein (ERα+) behave in a fundamentally different fashion than ERα-negative (ERα-) tumors with regard to their responses to hormonal therapy. Data obtained from both laboratory and clinical investigations suggested that some chemotherapeutic agents are clearly less effective in ERα+ tumors than ERα- tumors, although the mechanisms of ERα-mediated chemoresistance are not entirely clear. Moreover, recent studies from our laboratory and others demonstrated that the combination of antiestrogenic agents with chemotherapeutic drugs is of significant therapeutic benefit in ERα+ breast cancer over chemotherapy alone. In addition, the ERα-derived peptides, microRNAs specifically targeting ERα, as well as agents targeting estrogen-related receptors (ERRs) may hold promise to sensitize ERα+ breast tumors to chemotherapy. Considering that ERs are expressed in ˜ 65% of human breast cancer, the ERα-mediated chemoresistance has become a big challenge for clinical treatment. The hope to overcome this drug resistance relies on further clarification of specific pathways or molecules contributing to the resistance. More exhaustive and systematic studies are essential to reach deeper understandings on the underlying mechanisms and to develop novel approaches to sensitize ERα+ breast tumors to chemotherapy.

Interfacial Reaction in Aluminum/Carbon Multilayer Thin Films

The reaction at the interface between Al and amorphous C in Al/C multilayer thin films with modulation wavelengths of about 25nm and 125nm has been investigated by differential scanning calorimetry, X-ray diffraction, transmission electron microscopy/selected area electron diffraction and high resolution transmission electron microscopy. The reaction was found to take place in two steps. The first step onsets at about 300°C, and was identified as the diffusion of C into Al. The second step starts above 400°C, at a temperature strongly dependent on the modulation wavelength of the film, and is the formation of A14C3. The carbide has been observed to nucleate and grow inside the Al layers. The multilayer structure is preserved in the samples up to at least 550°C, and Al grains start to grow at or below 300°C.

Reversible twinning in pure aluminum

Twinning in metals is normally a permanent plastic deformation mechanism. Here we report reversible twinning in high stacking fault energy (SFE) aluminum. Twinning and spontaneous detwinning at the crack tip have been captured in situ during tensile straining under a transmission electron microscope. Both the in situ observation and the molecular dynamics simulations reveal a two-stage detwinning process. The high propensity for detwinning is due to the high SFE and the low frictional forces against the detwinning partial dislocations in Al. This discovery of reversible twinning has implications for the deformation of other high SFE materials.

Reversible movement of homogenously nucleated dislocations in a beta-titanium alloy

We demonstrate reversible movement of 1/2[11[over ]0](110) dislocation loops generated from nanodisturbances in a beta-titanium alloy. High resolution transmission electron microscope observations during an in situ tensile test found three reversible deformation mechanisms, nanodisturbances, dislocation loops and martensitic transformation, that are triggered in turn with increasing applied stress. All three mechanisms contribute to the nonlinear elasticity of the alloy. The experiments also revealed the evolution of the dislocation loops to disclination dipoles that cause severe local lattice rotations.

Tensile ductility and necking of metallic glass

Metallic glasses have a very high strength, hardness and elastic limit. However, they rarely show tensile ductility at room temperature and are considered quasi-brittle materials. Although these amorphous metals are capable of shear flow, severe plastic instability sets in at the onset of plastic deformation, which seems to be exclusively localized in extremely narrow shear bands approximately 10 nm in thickness. Using in situ tensile tests in a transmission electron microscope, we demonstrate radically different deformation behaviour for monolithic metallic-glass samples with dimensions of the order of 100 nm. Large tensile ductility in the range of 23-45% was observed, including significant uniform elongation and extensive necking or stable growth of the shear offset. This large plasticity in small-volume metallic-glass samples did not result from the branching/deflection of shear bands or nanocrystallization. These observations suggest that metallic glasses can plastically deform in a manner similar to their crystalline counterparts, via homogeneous and inhomogeneous flow without catastrophic failure. The sample-size effect discovered has implications for the application of metallic glasses in thin films and micro-devices, as well as for understanding the fundamental mechanical response of amorphous metals.

Ductile titanium alloy with low Poisson's ratio

We report a ductile beta-type titanium alloy with body-centered cubic (bcc) crystal structure having a low Poisson's ratio of 0.14. The almost identical ultralow bulk and shear moduli of approximately 24 GPa combined with an ultrahigh strength of approximately 0.9 GPa contribute to easy crystal distortion due to much-weakened chemical bonding of atoms in the crystal, leading to significant elastic softening in tension and elastic hardening in compression. The peculiar elastic and plastic deformation behaviors of the alloy are interpreted as a result of approaching the elastic limit of the bcc crystal under applied stress.

Nanostructured Ti-based multi-component alloys with potential for biomedical applications

A group of Ti(60)Cu(14)Ni(12)Sn(4)M(10) (M=Nb, Ta, Mo) alloys was prepared using arc melting and copper mold casting. The as-prepared alloys have a composite microstructure containing a micrometer-sized dendritic beta-Ti(M) phase dispersed in a nanocrystalline matrix. These new alloys exhibit a low Young's modulus in the range of 59-103 GPa, and a high yield strength of 1037-1755 MPa, together with large plastic strains. The combination of high strength and low elastic modulus offers potential advantages in biomedical applications.

Evolution of microstructures in materials induced by electropulsing

Nanostructures were formed in several conventional materials under single electropulsing, that is nanophases of alpha-Cu(Zn) and beta'-(CuZn) in a cold-worked alpha-Cu(Zn) alloy, nanosized gamma-Fe in a low-carbon steel, nanosized alpha-Al in a superduralumin, and orientated nanosized TiC in a TiC/NiCr cermet. The mechanisms responsible for the above nanostructured transitions can be attributed to the competition of many factors induced by electropulsing, including high-rate heating, thermal stress, reduced thermodynamic energy barrier and high-rate electron impacting. Also, many low-energy dislocation configurations, twins and stacking faults were formed in the copper alloy and cermet under the electropulsing. Such evolution of defects was associated with the electrical, thermal and stress energies induced by the electropulsing.

Enhanced diastereoselectivity in asymmetric crotylation reactions using propargylic dicobalt hexacarbonyl complexes

[reaction: see text] Hexacarbonyl dicobalt complexes of propargylic acetals undergo Lewis acid catalyzed crotylation reactions with enhanced levels of diastereoselectivity (dr 6 to >20:1, syn/anti) while efficiently producing stereochemically well-defined homoallylic ethers. These results are in contrast to uncomplexed propargylic acetals, which undergo the crotylation reactions with low selectivity (dr < 2:1, syn/anti). After removal of the cobalt complex, the reactions afford propargylic ethers in high yields.

Superheating of confined Pb thin films

In this work we report, for the first time, an experimental observation of a superheating phenomenon in metal thin films. By means of cold rolling, Pb thin films of about 20 nm thick were sandwiched by Al layers, and between them semicoherent epitaxial Pb/Al interfaces were formed. In situ x-ray diffraction analysis indicated that the confined Pb thin films could be superheated for at least 6 degrees C. Thermodynamic analysis indicated that such a substantial superheating in the confined two-dimensional thin films may originate from suppression of growth of the molten droplets by the epitaxial Al/Pb/Al confinement, instead of suppression of melt nucleation for the confined particle superheating.

Superplastic extensibility of nanocrystalline copper at room temperature

A bulk nanocrystalline (nc) pure copper with high purity and high density was synthesized by electrodeposition. An extreme extensibility (elongation exceeds 5000%) without a strain hardening effect was observed when the nc copper specimen was rolled at room temperature. Microstructure analysis suggests that the superplastic extensibility of the nc copper originates from a deformation mechanism dominated by grain boundary activities rather than lattice dislocation, which is also supported by tensile creep studies at room temperature. This behavior demonstrates new possibilities for scientific and technological advancements with nc materials.

[Determination of cadmium in soil slurry samples by GFAAS using ammonium oxalate as disperstant]

A method for the determination of trace cadmium in soil slurry samples by GFAAS was optimized. The factors that influence the performances of cadmium at different chemical modifier were investigated. The effect of background has also been studied. It is found that the slurry of soil samples was most stable with ammonium oxalate as disperstant. The results show that the determination of trace cadmium in soil slurry samples could performed.