Instrumented indentation technique (IIT) has been used to probe the phase-specific nanomechanical properties of heat treated 9Cr 1Mo ferritic martensitic (P9) steel. P9 steel was subjected to ...austenitization treatment, followed by water quenching, normalizing, furnace cooling, and subsequently tempering. Quantitative TEM analysis showed systematic changes in microstructure with variation in cooling rate in aforementioned heat treatments. Instrumented indentation tests were carried out at room temperature with a spherical indenter for evaluating hardness and elastic modulus. The yield strength of the steel from the load-displacement curves of cyclic indentation tests has been derived using neural networking method and yield parameter calculations. The properties derived from IIT using these methods were also validated with tensile test results. This work aims at correlating the local mechanical response measured by IIT with microstructural changes due to different heat treatments, which would be useful to extract mechanical properties of materials with heterogeneous microstructure.
Assessment of activation volume in 304L SS at high temperatures Christopher, J.; Singh, Balbir Kumar; Reddy, G.V. Prasad ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
12/2022, Letnik:
860
Journal Article
Recenzirano
The variation in apparent and true activation volumes of 304L SS with true plastic strain has been evaluated at three temperatures (973 K, 1073 K and 1123 K) over the strain rates of 3 × 10−3 s−1, ...3 × 10−4 s−1 and 3 × 10−5 s−1. The instantaneous strain rate sensitivity parameter was derived from strain-rate jump tests across different strain levels to estimate apparent activation volume. The values of apparent activation volume were higher at 973 K than at other temperatures. In contrast to the apparent activation volume, the estimated values of true activation volume using internal-stress-based kinetic rate law systematically increase with the increasing temperature from 973 K to 1123 K. The higher flow stress with a larger strain hardening rate at 973 K leads to a lower true activation volume in the steel compared to other temperatures. The model outcomes revealed that the instantaneous strain rate jump-up or jump-down leads to the change in the internal and effective stresses. The observed variations in geometrically necessary dislocation density (GND) and intra-grain reference orientation deviation (GROD) in the substructure substantiated the predicted variation in the internal stress level upon strain rate jump up/down. The true activation volume was estimated for a fixed value of mobile dislocation density (ρm = 5 × 1011 m−2) and for varying mobile dislocation density. Irrespective of ρm values, the estimated true activation volume values for 304L SS were in the order of 102 b3 to 103 b3, thereby implying that the intersection of dislocations coupled with the climb of jogged dislocations is the dominant mechanism during tensile deformation at high temperatures. Based on the analysis using the kinetic rate law with a fixed value of mobile dislocation density, it has been realized that the multiplication of effective stress and true activation volume remains constant across the plastic strain levels for the given combination of strain rate and temperature.
•In the range 973–1123 K, higher apparent activation volume ΔVapp was noticed at 973 K.•Estimated true activation volume (ΔVtrue) ranged from 370 b3–1200 b3.•In contrast to ΔVapp, ΔVtrue increases systematically with increasing temperature.•Effective stress (σe) increases with strain rate jump-up and decreases with jump-down.•For a fixed mobile dislocation density, the product of σe and ΔVtrue remains constant.
Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease characterized by production of autoantibodies and complex genetic inheritance. In a genome-wide scan using 85,042 SNPs, we ...identified an association between SLE and a nonsynonymous substitution (rs10516487, R61H) in the B-cell scaffold protein with ankyrin repeats gene, BANK1. We replicated the association in four independent case-control sets (combined P = 3.7 × 10−10; OR = 1.38). We analyzed BANK1 cDNA and found two isoforms, one full-length and the other alternatively spliced and lacking exon 2 (Δ2), encoding a protein without a putative IP3R-binding domain. The transcripts were differentially expressed depending on a branch point-site SNP, rs17266594, in strong linkage disequilibrium (LD) with rs10516487. A third associated variant was found in the ankyrin domain (rs3733197, A383T). Our findings implicate BANK1 as a susceptibility gene for SLE, with variants affecting regulatory sites and key functional domains. The disease-associated variants could contribute to sustained B cell-receptor signaling and B-cell hyperactivity characteristic of this disease.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Thermomechanical fatigue (TMF) studies were carried out on type 316 LN austenitic stainless steel (SS) base metal (BM) and its weld joint (WJ) with a temperature interval of 623–873 K under in-phase ...(IP) and out-of-phase (OP) combinations of mechanical strain and temperature. Tests were performed under mechanical strain control mode using the strain amplitudes in the range, ±0.25% to ±0.6%. Besides, isothermal low cycle fatigue (IF) tests were also conducted on the weld joint at 873 K. TMF cycling resulted in a slightly higher cyclic stress response (CSR) compared to IF loading for the weld joint. The IP TMF cycling yielded a higher plastic strain amplitude in comparison to OP TMF for both the base metal and the weld joint. Cyclic life of the weld joint is found to be inferior to that of the base metal. The fatigue lives exhibited by the base metal and the weld joint varied in the following sequence: IP TMF < IF < OP TMF. Preferential crack initiation in the weld region owing to embrittlement of transformed δ-ferrite was noticed with an increase in the mechanical strain amplitude under both TMF and IF cycling conditions. Crack initiation and propagation generally occurred in transgranular mode under IF and OP TMF and mixed (trans-plus intergranular) mode under IP TMF cycling. Electron back scattered diffraction (EBSD) measurements were employed to investigate the substructural development in terms of local misorientation distribution, inverse pole figure (IPF) maps and boundary dislocation density (ρ) in the weld metal region, under IF and IP TMF cycling. The dislocation density was found to decrease for both IF and IP TMF cycling compared to the as-welded condition, with the decrease being higher for IF cycling. The TMF data generated for the type 316LN SS base metal and weld joint at different strain ranges in the present study clearly demonstrated a lack of conservatism associated with the current design practice which is based on the IF data at the maximum temperature (Tmax) of the service cycle.
Country-specific reduced activation ferritic martensitic (RAFM) steels are being developed for fusion reactors by various countries. India has developed reduced activation ferritic martensitic steel, ...namely India specific reduced activation ferritic martensitic (INRAFM) steel (9Cr-1.4W-0.06Ta). In the present study, systematic investigations were carried out on this steel to identify the heat treatment parameters suitable for thermo-mechanical treatment by warm rolling. Subsequently, based on the identified parameters the steel was subjected to thermo-mechanical treatment at 973K and then air-cooled to room temperature without soaking. This was followed by tempering at 1033K for 90 min. Microstructure, dislocation density, hardness, and tensile properties of the steel were assessed in conventional normalized and tempered condition and thermo-mechanically treated plus tempered condition. The steel exhibits tempered martensitic structure decorated with M23C6 and MX precipitates with no traces of ferrite in thermo-mechanically treated plus tempered condition. Thermo-mechanical treatment has increased the dislocation density by three-fold compared to normalized and tempered condition. However, dislocations density decreased upon tempering due to recovery and annihilation processes. Hardness and tensile properties of the steel were significantly improved after thermo-mechanical treatment (without soaking) followed by tempering compared with the steel in normalized and tempered condition. Resultant microstructure and properties of the present steel were compared with those of a similar RAFM steel (9Cr-1.0W-0.06Ta) processed under identical conditions except that this steel was subjected to soaking for 30 min at thermo-mechanical treatment temperature. The INRAFM steel subjected to thermo-mechanical treatment (without soaking) portrays better tensile properties compared to RAFM steel subjected to thermo-mechanical treatment (with soaking) owing to absence of ferrite and presence of large number of finer M23C6 and MX precipitates in the former steel.
Creep deformation and rupture behaviour of a reduced activation ferritic-martensitic (RAFM) steel subjected to thermo-mechanical treatment (TMT) is studied and compared with those of conventional ...normalized and tempered (N + T) steel. In TMT processing, the steel is warm rolled and aged in austenite phase field at 973 K before the martensite transformation on cooling and is then tempered at 1038 K. The TMT processing renders the steel with higher dislocation density, refinement in lath structure and large quantity of finer M23C6 and MX precipitates than those in the N + T steel. Creep tests are carried out at 823 K over the stress range 180–300 MPa. TMT processing of the steel decreases its minimum creep rate (ε˙min) with corresponding increase in time to onset of tertiary stage of creep deformation, rupture life (tr) and creep rupture ductility (εf). The stress exponent value (n), obtained from minimum creep rate vs. stress plot, increases upon TMT processing, indicating high resistance to creep deformation than in the N + T steel. Resisting stress as estimated based on the Lagneborg and Bergman method is found to increase on TMT processing and is associated with high damage tolerance parameter, defined asλ=εf/(ε˙min.tr). Enhanced creep deformation and rupture strength of the TMT steel, compared to N + T steel, is attributed to the microstructural refinement. Post-creep microstructural investigations show higher microstructural stability of the steel on TMT processing and are in line with the observed high damage tolerance parameter (λ), longer time to onset of tertiary creep and rupture life.
•Creep behaviour of RAFM steel was investigated in N + T and TMT conditions.•TMT decreases minimum creep rate with increase in rupture life and ductility.•TMT results in increased stress exponent, damage parameter and resisting stress.•TMT imparts higher microstructural stability than N + T.
Herein we report the formulation of phenolic resin–based adhesive to join SiC substrates for a wide range of application temperatures. The formulation consists of phenolic resin as a binder and a ...mixture of B4C, Al2O3, Y2O3, Si, and SiO2 powders as active filler. The X‐ray diffraction, thermogravimetric analysis, porosity, and scanning electron microscopy analysis were carried out to understand the reactions occurring within this adhesive during its exposure to application temperatures. These results were also used to understand thermal stability and morphological changes that are involved in the formulated adhesive during its application. The shear strength values of lap joints of SiC substrates made with this phenolic adhesive after exposure to temperatures between 200 and 1500°C were studied to evaluate its adhesive capacity. Obtained SiC joints with this adhesive have shown an excellent lap shear strength value of 24 MPa after its cure. These joints were also found to be intact with good shear strength values of more than 5 MPa even after exposure to temperatures ranging from 200 to 1500°C. The results further confirm that the adhesive is potentially viable for joining SiC segments for their application at a wide range of temperatures in oxidative environments.
Representation of SiC/SiC joining made at low temperature using phenolic adhesive and the thermal stability of these joints at 1500°C.
Genome-wide association (GWA) studies revealed a number of single nucleotide polymorphisms (SNPs) significantly associated with type 1 diabetes (T1D). In an attempt to confirm some of these candidate ...associations, we genotyped 2046 Caucasian patients and 2417 normal controls from the United States for SNPs in five genomic regions. While no evidence was obtained for four genomic regions (rs2929366/NM_144715 on chromosome 3, rs9127/Q7Z4C4 on chromosome 5, rs1445898/CAPSL on chromosome 5 and rs2302188/NM_033543 on chromosome 19), we provide strong evidence for association between T1D and multiple SNPs in the IFIH1 linkage disequilibrium (LD) block on chromosome 2q. Among the 10 SNPs genotyped for the 2q region, four SNPs located within the IFIH1 gene or at the 5′ region of IFIH1 showed significant association with T1D in the Georgia population odds ratio (OR) = 1.7–1.9 with the best P-value found at SNP rs1990760 (P = 8 × 10−8 and OR = 1.9). Several SNPs outside of the IFIH1 gene also showed significant but weaker associations. Furthermore, IFIH1 gene expression levels in peripheral blood mononuclear cells are significantly correlated with IFIH1 genotypes, and higher IFIH1 levels are found in individuals with the susceptible genotypes (P = 0.005). Thus, both genetic association and gene expression data suggest that IFIH1 is the most plausible candidate gene implicated in T1D in this LD block.
Display omitted
•Strain hardening parameters differ between tensile and compressive branches of the loops.•In-phase cycling lives are markedly lower (i.e. 34–49%) than those under out-of-phase ...cycling.•Life reduction under in-phase cycling is significant (∼48.5%) at intermediate strain amplitudes.•Increase in strain amplitude decreases intergranular damage under in-phase cycling.•Design curves show a lack of conservatism for thermomechanical fatigue life estimate.
Thermomechanical fatigue (TMF) behavior of nitrogen enhanced 316LN stainless steel (with 0.14wt.% N) is investigated under in-phase (IP) and out-of-phase (OP) conditions at cyclic strain amplitudes of ±0.25 to ±0.8% and with a temperature interval of 623–873K. The study elucidates the differences in cyclic stress-strain response, TMF lives and fracture behavior of the material under IP and OP-TMF in the light of dynamic strain aging, thermal recovery and creep. The manifestations of these factors/phenomena are found to vary along stress-strain hysteresis loops, thereby leading to differences in cyclic strain hardening exponent (n′) and coefficient (K′) between the tensile and compressive branches of hysteresis loops. Irrespective of the imposed cyclic strain, transgranular fatigue failure is observed under OP-cycling in contrast to mixed-mode fracture under IP-cycling. The IP-cycling led to considerably lower cyclic life (i.e. 34–49%) compared to those under OP-TMF, with the life reduction being more significant (∼48.5%) at intermediate mechanical strain amplitudes of ±0.4 and ±0.6%. A comparison of the fatigue design curves under TMF with the corresponding isothermal fatigue curves (as per the RCC-MR design code) revealed a lack of conservatism in the latter.
Type 316LN stainless steel (SS) with varying nitrogen content (0.07, 0.14 and 0.22 wt%) was thermally aged at 873 K and 923 K for 20,000 h. The microstructures of thermally aged steels revealed ...secondary phases such as M23C6 carbides and Fe–Cr–Mo intermetallics at all the nitrogen contents and Cr2N nitrides additionally at 0.14 and 0.22 wt% N. The amount of precipitates increased with increase in nitrogen content and aging temperature. The effect of thermal aging on the tensile properties of 316LN SS was evaluated using automated ball indentation (ABI) technique at 298 K. The flow curves of the steels aged at 873 K were lower than those obtained under unaged condition. Whereas due to ageing at 923 K, the flow stress response gradually increased above the unaged condition with increasing nitrogen content. The ultimate tensile strength varied similarly at 873 K aging condition for all nitrogen levels and was observed to recuperate upon aging at 923 K, except for 0.07 wt% N. Yield strength was not strongly affected by thermal ageing, except the considerable increase in 316LN SS with 0.22 wt% N aged at 923 K. The addition of nitrogen generally imparted interstitial solid solution strengthening to 316LN SS. The higher the nitrogen content and ageing temperature, the higher is the precipitation strengthening due to ageing, which was reflected in the tensile behavior. Transmission electron microscopy examination of ABI deformed zone revealed dislocation-precipitate interactions, precipitate-shear band interaction and pile-up of dislocations at precipitates, influencing the tensile properties.
•Combined effect of ageing temperature and nitrogen content on 316LN SS was investigated using ABI technique.•The addition of nitrogen generally imparted interstitial solid solution strengthening to 316LN SS.•Evolution of precipitates on ageing 316LN SS at 873 K and 923 K for 20000 h are presented.•Higher the nitrogen content and ageing temperature, higher is the precipitation strengthening.•TEM studies on the plastic zone deformed under tip of ABI indenter are presented.
PDF
