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Oxide dispersion strengthened ferritic steel is considered an important structural material in fusion reactors due to its excellent resistance to radiation and oxidation. Fine and dispersed oxides can be introduced into the matrix via the powder metallurgy process. In the present study, large grain sizes and prior particle boundaries (PPBs) formed in the FeCrAlY alloy prepared via powder metallurgy. Thermo-mechanical treatment was conducted on the FeCrAlY alloy. Results showed that microstructure was optimized: the average grain diameter decreased, the PPBs disappeared, and the distribution of oxides dispersed. Both ultimate tensile strength and elongation improved, especially the average elongation increased from 0.5% to 23%.

The high tensile strength and irradiation resistance of oxide dispersion strengthened (ODS) ferritic steels is attributed to the ultrafine and dispersed oxides within the matrix. The high content of oxygen and yttrium is critical for the formation of dense Y-rich oxides. However, only few studies have reported the effect of oxygen content on the microstructure and mechanical properties of ODS steels. Herein, we employed gas atomization reactive synthesis to prepare pre-alloy powders and then hot isostatic pressing (HIP) to consolidate two 22Cr-5Al ODS steels with different oxygen content. Our results showed Y-rich precipitates at and near grain boundaries of the as-HIPed alloys. Moreover, with the oxygen content increasing from 0.04 to 0.16 wt%, more precipitates precipitated in the as-HIPed alloy, and the ultimate tensile strength of the alloy was improved. However, increasing the oxygen content to 0.16 wt% led to formation of stripe and chain precipitates at and near grain boundaries, which caused a partial intergranular fracture of the as-HIPed alloy.

We conducted field investigations, whole-rock geochemical, Sr-Nd and zircon U-Pb-Lu-Hf isotopic analyses on a suite of intrusive complex in the southern Nalati Range, SW Chinese Tianshan in order to better understand the Paleozoic tectonic and magmatic evolution of the belt. The intrusive complex comprises weakly foliated diorite, low-grade altered diabase, and deformed monzogranite; these plutonic rocks were in turn crosscut by undeformed coarse-grained diorite, granodiorite as well as granite stock. Foliated Late Silurian diorites (421 ± 4 Ma) show arc-type geochemical features, slightly negative whole-rock eNd(t) value (− 1.7; T DM-Nd = 1.52 Ga) and variably positive zircon eHf(t) values (2.34 to 7.27; T DM-Hf : 0.95– 1.26 Ga). Deformed Early Devonian porphyritic monzogranites (411 ± 4 Ma) show geochemical features similar to A-type granite, and their zircon eHf(t) values range from − 6.63 to 1.02, with T DM-Hf ages of 1.82 to 1.33 Ga. Metamorphosed Early Devonian diabases (ca. 410 Ma) have OIB-like REE patterns, eNd(t) values of − 2.0 ~ − 0.8 and T DM-Nd ages of 1.37– 1.25 Ga. The undeformed Early Carboniferous diorite and granodiorite (353– 344 Ma) exhibit arc-type geochemical features, positive eHf(t) values of 6.11– 7.91 with T DM-Hf ages of 0.97– 0.86 Ga, and positive eNd(t) value of 1.9 with T DM-Nd age of 1.04 Ga. The Early Permian granite stock (292 ± 5 Ma) has highly differentiated REE pattern, slightly negative eNd(t) value (− 4.4) and variable zircon eHf(t) values of − 9.73– 6.36. Combining with available data, Early Paleozoic (500– 410 Ma) arc-related magmatic rocks occurring on both sides of the suture zone along the southern Nalati Range, likely resulted from a bi-directional subduction of the Paleo-Tianshan Ocean beneath the Yili Block to the north and the Central Tianshan to the south. Occurrences of A-type granites and OIB-like diabases (ca. 410 Ma) along the Nalati Range likely indicate a hot extensional regime probably induced by the break off of the northward subducting slab of the Paleo-Tianshan Ocean. The closure of the Paleo-Tianshan Ocean and subsequent amalgamation during Early Carboniferous resulted in the regional deformation and metamorphism of the Early Paleozoic arc-related magmatic rocks. From Early to Late Carboniferous, a magmatic arc that corresponded to the well-developed Late Paleozoic Balkhash-Yili active continental margin, superimposed upon the southern Yili Block, most likely resulted from the southward subduction of the Junggar-North Tianshan Ocean. After the closure of the North Tianshan Ocean in Late Carboniferous, the study area was dominated by post-orogenic magmatism.

The Chinese Central Tianshan constitutes the centric and vital component of the Tianshan orogen, it contains important information for understanding the accretionary orogeny of the Central Asian Orogenic Belt (CAOB). To better constrain the Paleozoic evolution of the Chinese Central Tianshan, we present new field observations, fabric analyses, zircon U–Pb ages, zircon Lu–Hf isotopic and whole rock geochemical data of mafic, intermediate and felsic intrusive rocks in the Baluntai area, Chinese Central Tianshan. Field-scale and microscopic structural patterns of the intrusive rocks reveal that the early Paleozoic gabbro-diorite intrusions underwent multistage structural reworking, and generally exhibit gently south- or north-dipping foliations and microscopic kinematic fabrics indicating top-to-the-north shearing. These ductilely deformed intrusive rocks were intruded by granitic sills or dikes that are generally sub-parallel or with low angle to the main foliations of the host rocks. Gentle foliations and top-to-the-north kinematics can be rarely noticed within the granitic intrusions. At the sites close to the Baluntai Fault, locally intense mylonitization occurred in the felsic intrusions and deformed mafic-intermediate ones, where earlier shallow foliations were completely or partially transformed to steep ones bearing sub-horizontal stretching lineations, and asymmetric kinematic indicators suggest dextral shearing. Zircon LA-ICP-MS U–Pb datings constrain the emplacement ages of the gabbroic and dioritic intrusive rocks at 452–420 Ma, and the crystallization age of one mylonitic K-granite at 417 Ma. Two samples of granitic sill contain plenty of zircons inherited from the host gabbroic and dioritic rocks, and a few such zircons have dark rims probably formed during granitic injection, dating on these rims roughly constrains the crystallization ages of the felsic sills at ca. 370–360 Ma. The eHf(t) values of a gabbro (420 Ma), two diorite samples (425 and 445 Ma) and a mylonitic granite (417 Ma) vary from −15.45 to −2.06, corresponding to two-stage crustal model ages (TDM)C ranging from ∼2.4 Ga to ∼1.5 Ga, suggesting variable degrees of involvement of the Proterozoic crustal basement and the juvenile mantle components during the early Paleozoic magmatic generation. The geochemical data of the mafic-intermediate plutons exhibit features of magmatic rocks formed in continental arcs. The mylonitic granite and one undeformed granite resemble A-type granite in terms of geochemical features, suggesting that these granites were produced in a post-collisional/extensional environment. Considering the previously published data, the early Paleozoic arc-type magmatic rocks within the Chinese Central Tianshan likely resulted from the southward subduction of an oceanic basin located to the north, and ceased progressively during 420–400 Ma. The amalgmation between Chinese Central Tianshan and Tarim most likely completed at ca. 360 Ma following the closure of the South Tianshan back-arc basin. This event reworked the Chinese Central Tianshan arc and formed the top-to-the-north kinematics. Thereafter, the Chinese Central Tianshan was affected by the early Permian dextral strike-slip faulting due to the regional large-scale transcurrent tectonics and overprinted by the Permian mafic magmatism.

The northern part of the Yili Block, located in the northwest of the Chinese Tianshan, extends westward to joint with the Aktau-Junggar domain in Kazakhstan, and is one of the major continental constituents of the Central Asian Orogenic Belt (CAOB). The nature and tectonic significance of the basement of the continental domains are important for understanding the continental evolution and geodynamic processes of the CAOB. We investigated the Wenquan metamorphic complex (WMC) that represents the basement and metamorphosed sedimentary cover of the northern Yili Block. The WMC is mainly composed of gneissic S-type granite, migmatite associated with amphibolite, paragneiss, micaschist, quartzite, marble, and intruding leucogranitic dykes. The migmatites display banded, schlieren and ptygmatic structures containing rootless, lensoid or layered leucosome and leucocratic sills, which are indicative of in situ partial melting of the country rocks and variable degrees of melt migration. Geochemical data suggest that the protoliths of the orthogneiss and gneissic K-granite belong to peraluminous S-type granites characterized by wide range of I (Sr) values (0.68324–0.72365), low ɛ Nd ( t ) values (−1.9 to −4.4) and two-stage Nd model ages ( t MD -2: 1.56–1.82 Ga). The S-type granites might have derived from both clay-poor and clay-rich source rocks that are probably meta-sedimentary and meta-volcanic rocks in the WMC. The leucogranites show relatively narrow range of I (Sr) values (0.70273–0.70419), more negative ɛ Nd ( t ) values (−6.9 to −9.1) and more consistent t MD -2 ages (1.51–1.55 Ga). The leucosome and leucocratic sills show variable Sr and Nd isotopic compositions probably due to localized and different degree of partial melting. Our new zircon SHRIMP and LA-ICPMS U–Pb ages, together with previously published data indicate that the migmatization occurred at 926–909 Ma, the gneissic S-type granites emplaced during 919–862 Ma, and the leucogranites emplaced in the period of 909–845 Ma. Inherited old zircons were found in all dated samples and may have come from their source rocks. Association of geochronologically overlapped and genetically linked migmatites, gneissic S-type granites and leucogranitic rocks is interpreted as the results of anatexis of the upper crustal rocks during an early Neoproterozoic tectonic/metamorphic event that needs to be further studied in the northern Yili Block. Such early Neoproterozoic migmatization and S-type granitic magmatism are considered as an important episode of reworking and cratonization of the continental crust of the Yili and adjacent continental blocks in Central Asia.

The tectonic affinity and structural evolution of the South Tianshan are key issues to understand the Paleozoic accretionary or collisional orogenesis in the southwestern Central Asian Orogenic Belt, but remain controversial. Geological and structural investigations on the Early Paleozoic low-grade metamorphic volcanic-sedimentary sequences around the Bayinbuluk basin demonstrate that they were prevalently reworked by north-vergent ductile deformation and overlain unconformably by Devonian to Carboniferous carbonates. Zircon U–Pb dating indicates that the volcanic rocks erupted during the Middle Ordovician to Early Devonian time (460–410 Ma), and contain Neoarchean to Neoproterozoic zircon xenocrysts (~2.75 Ga, ~2.46 Ga, ~1.60 Ga, 997–963 Ma and 827 Ma). Their whole-rock elemental, Sr–Nd isotopic (eNd(t) = −5.0 to +3.6) and zircon Lu–Hf isotopic (eHf(t) = −13.5 to +11.6) features resemble those of Andean-type continental arc volcanic rocks. The coexisting tuffaceous sedimentary rocks indicate a depositional environment amidst a continental volcanic arc at 421 to 404 Ma. The newly obtained and available geochronological, geochemical and structural data suggest that: (1) a wide active continental margin covering the South and Central Tianshan and northern Tarim was formed due to Early-Mid Paleozoic southward subduction of the Paleo-Tianshan Ocean beneath the Tarim Craton; and (2) a Mid-Paleozoic transition from advancing to retreating accretionary orogeny was followed by opening of the South Tianshan back-arc basins and break-up of the northern Tarim continental margin. The South Tianshan was subsequently subjected to regional deformation during the successive diachronous closure of the major and back-arc oceanic basins, and locally reworked by the ductile strike-slip faulting (307–255 Ma).

The South Tianshan is located to the north of the Tarim block and defines the southern margin of the Paleozoic Central Asian Orogenic Belt (CAOB). This study presents new structural data, geochronological and geochemical results for the Wuwamen ophiolite mélange in the Chinese segment of the South Tianshan. In the south, the Wuwamen ophiolite mélange shows typical block-in-matrix fabrics and occurs in the footwall of a south-dipping thrust fault, hanging wall of which is composed of weakly metamorphosed and deformed Lower Paleozoic marine to deep marine sequences from the South Tianshan. In the north, a southdipping thrust fault juxtaposes the Wuwamen ophiolite mélange in its hanging wall against the high-grade and strongly deformed metasedimentary rocks from the Central Tianshan in its footwall.

International audience; Permian large-scale transcurrent tectonics and massive magmatism are prominent features of the Tianshan belt and neighboring regions of the Central Asian Orogenic Belt. Structural, geochronological and geochemical analyses of Carboniferous and Permian intrusive rocks associated with the Kangguer-Huangshan Shear Zone (eastern Chinese North Tianshan) provide constraints on their tectonic setting and the tectonic evolution of the Tianshan belt as well. Carboniferous granitic rocks were emplaced at 338 4 Ma and 347 2 Ma, respectively, and show geochemical features typical of the calc-alkaline series. These arc-type granites do not display ductile deformation, probably because they were completely cooled at the time of shearing tectonics, and are only offset by brittle strike-slip faults. In contrast, Permian granitoids display pervasive ductile tectonic features diagnostic of synkinematic emplacement. Four gabbro and diorite samples from the East Huangshan intrusive complex yielded zircon U-Pb ages of 267 to 275 Ma, and a granitic dike is dated at 290 1 Ma. The granitic dike is cut by en-echelon right-lateral strike-slip faults, and the mafic intrusive complex displays a sigmoidal shape with mylonitic foliation localized at its margins. Other specific pluton shapes (such as tongue and tadpole-like) and synmagmatic deformation can be observed in intrusions of the same age, showing similar fabrics and kinematics consistent with that of the Kangguer-Huangshan Shear Zone. Numerous mafic to felsic dikes occur within and off the shear zone with a dominant SE-NW orientation and minor varieties in N-S or NNE-SSW directions. One gabbro dike that intrudes the early Carboniferous granite of the East Kanggurtag area yielded a magmatic age of 274 4 Ma, and contains older zircons ( 340 Ma, 390 Ma, 450 Ma, and 1.3-2.2 Ga) probably inherited from intruded rocks. The Permian intrusive rocks have variable chemical compositions suggesting derivation of these rocks from depleted and undepleted (or enriched) mantle sources with involvement of subductionrelated components. We conclude from our integrated analysis of the geological, structural, geochemical and geochronological data that the Permian magmatic rocks were formed in a post-collisional/post-orogenic setting from multiple sources, and were emplaced under the control of large-scale dextral transcurrent tectonics.