Grain boundary network evolution in electron-beam powder bed fusion nickel-based superalloy Inconel 738

Additive manufacturing (AM) of alloys has attracted much attention in recent years for making geometrically complex engineering parts owing to its unique benefits, such as high flexibility and low waste. The in-service performance of AM parts is dependent on the microstructures and grain boundary networks formed during AM, which are often significantly different from their wrought counterparts. Characteristics such as grain size and morphology, texture, and the detailed grain boundary network are known to control various mechanical and corrosion properties. Advanced understanding on how AM parameters affect the formation of these microstructural characteristics is hence critical for optimising processing parameters to unlock superior properties. In this study, the difficult-to-weld nickel-based superalloy Inconel 738 was fabricated via electron-beam powder bed fusion (EPBF) following linear and random scanning strategies. Random scanning resulted in finer, less elongated, and crystallographically more random grains compared to the linear strategy. However, both scanning strategies achieve unique high grain structure stability up to 1250 ℃ due to the presence of carbides pinning the grain boundaries. Despite significant difference in texture and morphology, majority of grains terminated on {100} habit planes in both linear and random built samples. The results show potential for controlling grain boundary networks during EPBF by tuning scan strategies

Nano-twining and deformation-induced martensitic transformation in a duplex stainless steel 2205 fabricated by laser powder bed fusion

Duplex stainless steels (DSSs) possess desirable combinations of mechanical properties and excellent corrosion resistance due to their composition and equilibrium microstructure of roughly equivalent fractions of ferrite and austenite. They are used in harsh environments such as marine infrastructures, oil & gas, and paper & pulp industries. Components with complex geometries are often required for these applications. Additive manufacturing (AM) techniques such as laser powder bed fusion (LPBF) can be harnessed to fabricate components with greatest complexity. However, AM fabrication is well-known to promote non-equilibrium microstructures with high dislocation densities and Cr2N precipitates, resulting in inferior ductility. This is generally regarded as a challenge, however, short heat treatments of such as-built microstructures have been shown to attain refined duplex equilibrium microstructures. Recently, annealed LPBF DSS 2205 has been reported to possess strength higher than wrought counterparts and ductility properties better than the as-built state. However, the microstructural phenomena and deformation mechanisms behind these attractive properties remain poorly understood. Through multi-scale microstructural characterization, we show that the improved strength results not only from the hard ferrite phase, but also fine austenite grain size and nanoscale oxide dispersion strengthening. The enhanced ductility may be attributed to a combination of deformation mechanisms including dislocation slip, stacking fault formation, deformation twinning, and a deformation-induced martensitic transformation. We discuss how the level of microstructural complexity and solid-state phase transformations during LPBF and annealing can unlock multiple strengthening mechanisms during tensile deformation. Such fundamental understanding is crucial for designing AM parts with reproducible and optimised mechanical properties

Evidence of in-situ Cu clustering as a function of laser power during laser powder bed fusion of 17–4 PH stainless steel

The use of intrinsic heat treatments to control the microstructural evolution during additive manufacturing could eliminate the need for costly post-build processing. Using atom probe microscopy and cluster search algorithms, this study investigates the degree of Cu clustering and precipitation in 17–4 precipitate hardening (PH) stainless steel fabricated by laser powder bed fusion (LPBF). It was found that LPBF samples exhibit a greater than random degree of Cu clustering, irrespective of the laser power during fabrication. It is further shown that using a higher laser power (161.5 W rather than 127.5 W) led to a higher number density of Cu clusters, Cu precipitates, and higher hardness due to the greater heat input. The observations of Cu-rich clusters and precipitates within as-printed LPBF samples and its laser power dependence are novel and show potential for inducing desired strengthening phases directly during LPBF, mitigating the need for post-fabrication heat treatments

Effect of compositional variations on the heat treatment response in 17-4 PH stainless steel fabricated by laser powder bed fusion

17–4 precipitate hardening (PH) stainless steel is used in various applications including in the aerospace, marine, and chemical industries, largely due to its unique combination of corrosion resistance and high strength, which is achieved by the formation of nanoscale Cu-rich precipitates during aging. 17–4 PH has been widely researched for its applicability for laser powder bed fusion (LPBF). However, there are discrepancies in the literature on its heat treatment response, which seem to be linked to compositional variations. Systematic studies of the interplay between these variations and nanoscale precipitation are currently missing. Using atom probe tomography, we present a systematic study of the heat treatment responses of two variants of LPBF 17–4 PH builds fabricated from different powder feedstocks, with significant differences in N contents (High vs Low N 17–4). Both variants formed predominantly δ-ferritic as-built microstructures. The as-built High N 17–4 variant showed a higher volume fraction of austenite which further increased upon solution annealing and quenching. The consequence was no appreciable hardening effect due to the absence of Cu precipitation in either austenite or martensite after aging, degrading the alloy's desirable property profile. Conversely, Low N 17–4 showed no austenite in the as-built condition and a fully martensitic matrix after solution annealing. This variant had the desired aging response; a ∼ 140 HV 5 increase in hardness due to nanoscale Cu precipitation. Our findings describe the deleterious effects of compositional variations incurred during the LPBF process flow and how they can be overcome in 17–4 PH and similar steels

Correlation of microstructure, mechanical properties, and residual stress of 17-4 PH stainless steel fabricated by laser powder bed fusion

17-4 precipitation hardening (PH) stainless steel is a multi-purpose engineering alloy offering an excellent trade-off between strength, toughness, and corrosion properties. It is commonly employed in additive manufacturing via laser powder bed fusion owing to its good weldability. However, there are remaining gaps in the processing-structure-property relationships for AM 17-4 PH that need to be addressed. For instance, discrepancies in literature regarding the as-built microstructure, subsequent development of the matrix phase upon heat treatment, as well as the as-built residual stress should be addressed to enable reproducible printing of 17-4 builds with superior properties. As such, this work applies a comprehensive characterisation and testing approach to 17-4 PH builds fabricated with different processing parameters, both in the as-built state and after standard heat treatments. Tensile properties in as-built samples both along and normal to the build direction were benchmarked against standard wrought samples in the solution annealed and quenched condition (CA). When testing along the build direction, higher ductility was observed for samples produced with a higher laser power (energy density) due to the promotion of interlayer cohesion and, hence, reduction of interlayer defects. Following the CA heat treatment, the austenite volume fraction increased to ∼35 %, resulting in a lower yield stress and greater work hardening capacity than the as-built specimens due to the transformation induced plasticity effect. Neutron diffraction revealed a slight reduction in the magnitude of residual stress with laser power. A concentric scanning strategy led to a higher magnitude of residual stress than a bidirectional raster pattern

New insights into the character of austenite-ferrite boundaries in an additively manufactured duplex stainless steel

The crystallography and chemistry of interfaces between austenite and ferrite in duplex steels control many important materials properties but remain poorly understood. In this study, we experimentally show that in an additively manufactured and heat treated duplex stainless steel, the majority of austenite-ferrite interfaces terminate on {111}A/{110}F planes, and this behaviour is more pronounced for rational interfaces with the Kurdjomov-Sachs orientation relationship. Interface segregation was found to be controlled by not only the interface crystallography but also the bonding properties of solute atoms. Solute elements showed higher interfacial excess at irrational interfaces. Furthermore, a heterogeneous distribution of selected solute elements in austenite-ferrite interfaces planes was observed. Our findings reinforce the importance and, in fact, necessity to consider five independent crystallographic parameters and chemical architecture of interphase boundaries for advanced control of mechanical and other critical properties in duplex materials

Psychometric precision in phenotype definition is a useful step in molecular genetic investigation of psychiatric disorders

Affective disorders are highly heritable, but few genetic risk variants have been consistently replicated in molecular genetic association studies. The common method of defining psychiatric phenotypes in molecular genetic research is either a summation of symptom scores or binary threshold score representing the risk of diagnosis. Psychometric latent variable methods can improve the precision of psychiatric phenotypes, especially when the data structure is not straightforward. Using data from the British 1946 birth cohort, we compared summary scores with psychometric modeling based on the General Health Questionnaire (GHQ-28) scale for affective symptoms in an association analysis of 27 candidate genes (249 single-nucleotide polymorphisms (SNPs)). The psychometric method utilized a bi-factor model that partitioned the phenotype variances into five orthogonal latent variable factors, in accordance with the multidimensional data structure of the GHQ-28 involving somatic, social, anxiety and depression domains. Results showed that, compared with the summation approach, the affective symptoms defined by the bi-factor psychometric model had a higher number of associated SNPs of larger effect sizes. These results suggest that psychometrically defined mental health phenotypes can reflect the dimensions of complex phenotypes better than summation scores, and therefore offer a useful approach in genetic association investigations

Thunderclap headache triggered by micturition: responsive to nimodipine

Primary thunderclap headache (TCH) is a rare condition, of which the onset can be triggered by coughing, exercise, and sexual activity. Micturition is a recognized trigger of secondary TCH with pheochromocytoma in bladder, but not of primary TCH. We describe a patient with an apparent primary TCH, which repeatedly occurred immediately after micturition until she achieved a therapeutic dosage of nimodipine

Systemic delivery of microRNA-101 potently inhibits hepatocellular carcinoma in vivo by repressing multiple targets

Targeted therapy based on adjustment of microRNA (miRNA)s activity takes great promise due to the ability of these small RNAs to modulate cellular behavior. However, the efficacy of miR-101 replacement therapy to hepatocellular carcinoma (HCC) remains unclear. In the current study, we first observed that plasma levels of miR-101 were significantly lower in distant metastatic HCC patients than in HCCs without distant metastasis, and down-regulation of plasma miR-101 predicted a worse disease-free survival (DFS, P<0.05). In an animal model of HCC, we demonstrated that systemic delivery of lentivirus-mediated miR-101 abrogated HCC growth in the liver, intrahepatic metastasis and distant metastasis to the lung and to the mediastinum, resulting in a dramatic suppression of HCC development and metastasis in mice without toxicity and extending life expectancy. Furthermore, enforced overexpression of miR-101 in HCC cells not only decreased EZH2, COX2 and STMN1, but also directly down-regulated a novel target ROCK2, inhibited Rho/Rac GTPase activation, and blocked HCC cells epithelial-mesenchymal transition (EMT) and angiogenesis, inducing a strong abrogation of HCC tumorigenesis and aggressiveness both in vitro and in vivo. These results provide proof-of-concept support for systemic delivery of lentivirus-mediated miR-101 as a powerful anti-HCC therapeutic modality by repressing multiple molecular targets. © 2015 Zheng et al.published_or_final_versio

Mammalian Genes Preferentially Co-Retained in Radiation Hybrid Panels Tend to Avoid Coexpression

Coexpression has been frequently used to explore modules of functionally related genes in eukaryotic genomes. However, we found that genetically interacting mammalian genes identified through radiation hybrid (RH) genotypes tend not to be coexpressed across tissues. This pattern remained unchanged after controlling for potential confounding factors, including chromosomal linkage, chromosomal distance, and gene duplication. Because >99.9% of the genetically interacting genes were identified according to the higher co-retention frequencies, our observation implies that coexpression is not necessarily an indication of the need for the co-presence of two genes in the genome, which is a prerequisite for cofunctionality of their coding proteins in the cell. Therefore, coexpression information must be applied cautiously to the exploration of the functional relatedness of genes in a genome