查看更多>>摘要：A cold NiTiTa alloy was found to be very brittle in the fully annealed condition due to its high-austenite stability, which suppressed stress-induced-martensite transformation and dislocation slip. However, ductility and super-elasticity are largely improved by formation of Ti3Ni4 and Ti2Ni3 precipitates upon aging at lower temperatures. Cold work promotes Ti2Ni3 precipitation during aging. Compared to the as-drawn material, the fully annealed material shows higher strain recovery and elongation after aging for a short amount of time.
查看更多>>摘要：A novel technique, deformation-driven metallurgy (DDM), was proposed to obtain high-quality tungsten-copper composites based on the principle of severe plastic deformation. A homogeneous distribution of ultrafine tungsten particles improved the continuity of tungsten-copper system. The wear resistance and arc-erosion resistance of DDM composites with superior density and hardness were enhanced by 48.3 and 46.6 pct, respectively.
查看更多>>摘要：We report the first observation of isothermal phase separation triggered by inwardly diffusing interstitial nitrogen atoms during nitriding of an equiatomic FeNiCo medium entropy alloy. Detailed microstructural characterization revealed a phase-separated microstructure within the nitrided region containing two FCC solid solution phases with one enriched in Fe and N while other enriched in Co and Ni. This demonstrates the potential utilization of interstitial N alloying to tailor the microstructure of multi-principal element alloys.
查看更多>>摘要：The reduction of freckle defect in the single-crystal blade root by controlling local cooling conditions was investigated. Application of the IRBs technique increased the temperature gradient from about 10 to 21 K/cm, thus reducing PDAS in the root compared to the standard Bridgman process. Refinement of the microstructure and reduction of the curvature of the liquidus isotherm resulted in mitigation or elimination of freckle in the area near the root edge.
ROSA ORTEGA-REYESFRANCISCO A. PEREZ GONZALEZJAVIER H. RAMIREZ-RAMIREZ
7页
查看更多>>摘要：The changes occurring in two heat-resistant alloys while aged at 750 °C for different periods of time were studied. Aging promoted precipitation of secondary M_(23)C_6 carbides and transformation of Nb-rich, which were evaluated by SEM. The results show that transformation of the NbC starts from their boundaries to their centre by silicon diffusion; carbon was detected to migrate from these particles promoting precipitation of secondary Cr-rich carbides in regions adjacent to the Nb-rich particles.
查看更多>>摘要：Martensite-austenite constituents (M/A) decomposed from intercritical austenite in the coarse grain heat-affected zone (CGHAZ) affect the mechanical properties of welded steel pipelines. This work reports a quantitative investigation of intercritical austenite formation and its decomposition in the CGHAZ of an X80 line pipe steel through simulated welding thermal excursions, dilatometry, and metallography. The evolution of microstructure which involves austenite formation, a transformation stasis, and decomposition was revealed and used to rationalize the observation that only 0.05 to 0.1 M/A fraction is typically found in industrial welds.
查看更多>>摘要：In the present research work, an effort has been made to examine the effect of the ERNiCrCoMo-1 filler on solidification mechanism, microstructural characterization, welded joint integrity, and residual stresses of the dissimilar welded joint (DWJ) of martensitic grade P92 steel and Ni-based superalloy Inconel 617 for advanced ultra-supercritical (A-USC) power plant application. Weld joints have been fabricated for V groove geometry by using the multipass gas tungsten arc welding (GTAW) process. The multiple aspects of the welded joint structural integrity have been tested by performing the tensile test, microhardness tests and Charpy impact test. The ERNiCrCoMo-1 weld solidified in austenitic mode with columnar and cellular dendrites in the interior region, while columnar dendrites were observed near the interface region. The unmixed zone (UZ) formation was noticed at the ERNiCrCoMo-1 filler weld and P92 steel interface, while the UZ gets eliminated at Inconel 617 interface. The microstructural observation near the interface showed that migrated grain boundaries were observed frequently near the lower region of the weld metal (WM), while at the interface of the P92 steel and ERNiCrCoMo-1 filler welds, higher density of soft 3 ferrite patches for the capping and backing passes were observed. The energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) results confirmed the presence of the Cr- and Mo-enriched M_(23)C_6 precipitates, Mo-enriched M_6C and Ti-enriched Ti(C, N) precipitates in the WM. Acceptable mechanical properties were obtained at room temperature. The Charpy impact toughness (CIT) was observed 98 ± 5 J and 108 ± 3 J for WM with V notch at the top and root region, respectively. The dramatic reduction in CIT was after the postweld heat treatment (PWHT) was attributed to the evolution of the carbide particles in interdendritic areas. Tensile strength results of the cross-weld specimen showed the tensile strength value marginally lower than the P92 steel but significantly lower than the Inconel 617 base metal in both as-welded (AW) and PWHT condition along with fracture in the week region of P92 steel. The failure from the region of P92 steel instead of the ERNiCrCoMo-1 filler WM confirmed that the welded joint was safe for A-USC power plants boiler application. A significant heterogeneity in microhardness was seen along the weldments with a peak hardness of 445 ± 8 in P92 CGHAZ and a lower hardness of 181 HV in the peninsula. The increase in microhardness of the WM as a result of PWHT was attributed to the evolution of the carbide particles in the WM. Through thickness residual stresses variation was also measured for both WM and HAZ region and the effect of the PWHT on the magnitude and nature of the residual stresses were also performed. Hence the work provides insight into welding procedure development, microstructural evolution in the WM and HAZ, variation in mechanical properties, and residual stresses variation for the welded joint of P92 steel and Inconel 617 alloy.
查看更多>>摘要：Cr atoms can promote the formation of icosahedral short-range order (ISRO) in Al-Zn alloy liquid, which is believed to be the structural origin of the quasicrystal (QC) phase in the assumption of a QC-enhanced nucleation mechanism. However, this claim still lacks experimental evidence. In this work, we investigate the liquid structure of Al-Zn and Al-Zn-Cr alloys through high-energy X-ray diffraction at a synchrotron facility. The constrained reverse Monte Carlo simulation method is used to obtain the three-dimensional atomic configuration. The results show that the Cr addition reduces the formation of Al-centered ISRO and increases the formation of Zn-centered ISRO. Large amounts of ISRO or high five-fold symmetry are found around Cr atoms. Furthermore, the correlation between Al and Zn atoms is significantly changed due to the Cr addition. The pentagon-rich Al-centered and Cr-centered clusters show a strong tendency to aggregate and build interpenetrating structures on a medium-range scale. The icosahedral medium-range order (IMRO) will form through the linkage of vertex-, edge-and intercross-shared types of the Cr-centered icosahedra or icosahedra-like clusters. In particular, an IMRO structure with a composition similar to the Al_(45)Cr_7 phase is found, which is considered the intermediate phase of fcc-Al nucleation. These findings may provide structural hints of the QC-enhanced nucleation mechanism.
查看更多>>摘要：Ni-Mo-Cr3C2 system coatings with the different Cr3C2 mass fractions were prepared on GCr15 bearing steel by laser cladding (LC). The microstructure and phases of obtained coatings were analyzed using an ultra-depth of field microscope (UDFM) and X-ray diffractometer (XRD), respectively. The friction-wear performance of Ni-Mo-Cr3C2 coatings under the grease-lubrication condition was investigated using a ball-disc-wear test, and the wear mechanism was also discussed. The results show that the Ni-Mo-Cr3C2 coatings have a strong dendritic structure, in which the Cr3C2 with the spherical shape is distributed on the coatings. The hardness of Ni-Mo-5Cr(3)C(2), -15Cr(3)C(2) and -25Cr(3)C(2) coatings is 990 +/- 29, 1018 +/- 33, and 1316 +/- 27 HV0.5, respectively, higher than 540 +/- 30 HV0.5 of substrate. The average coefficients of friction (COFs) of Ni-Mo-5Cr(3)C(2), -15Cr(3)C(2) and -25Cr(3)C(2) coatings are 0.12 +/- 0.07, 0.11 +/- 0.05, and 0.10 +/- 0.04, respectively, and the corresponding wear rates are 71.9 +/- 3.3, 40.1 +/- 2.4, and 19.9 +/- 2.7 mu m(3) s(-1) N-1, respectively, which decrease with the increase of Cr3C2 mass fraction. The reinforcing phase of Cr3C2 exhibits the excellent performance of friction reduction, which also further improves the wear resistance. Moreover, the grease storage in the pores plays the role of friction reduction, in which the lubrication effect of round-edged pores is better than that of sharp-edged pores.
查看更多>>摘要：The effect of 0.03 and 0.08 at. pct Fe additions on the formation of secondary phases in an Al-1.1Mg-0.5Cu-0.3Si at. pct alloy was investigated. Following solution heat treatment and natural aging, the alloys were analyzed in an undeformed, artificially aged condition and in a two-step deformed condition consisting of 80 pct deformation, artificial aging, 50 pct deformation and a final, short artificial aging. Using electron microscopy, it was found that both alloys contained similar amounts of primary Mg2Si particles, while the higher Fe level alloy produced roughly twice the number density and volume fraction of primary bcc alpha-AlFeSi particles. Lower volume fractions of hardening precipitates were measured in the high Fe level alloy, as attributed to the lower amount of Si available for precipitation. Using atomic resolution scanning transmission electron microscopy, a mix of L phases and structural elements of GPB zones was found in the undeformed conditions. In the deformed conditions, scanning precession electron diffraction revealed that the precipitates were nucleated both on and between deformation induced defects. The addition of Fe affected the relative ratio of these precipitates. Hardness measurements of conditions combining deformation and artificial aging were performed to investigate the hardening mechanisms at each processing step.
NSTL
Springer Nature