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Additive manufacturing of metallic parts by Selective Laser Melting (SLM) implies high temperature gradients and small volume of the melt bath. These conditions make the process scales close to those available for state-of-the-art massively parallel atomistic simulations. In the paper, the microscopic mechanisms responsible for the formation of primary microstructure during molten metal solidification are investigated using classical molecular dynamics (CMD). The 316L austenitic stainless steel with face centred cubic lattice, which is widely used in industry including SLM applications was chosen as a material for the CMD simulations. It was shown that solidified material inherits substrate defects and catches new ones, which interact with the solidification front thus producing the primary microstructure. Peculiarities of solidification in different crystallographic directions and solidification front interaction with grain boundaries and newly produced defects (mostly twin boundaries) as well as their formation are under study. Resulting microstructures of virtual samples are compared with those of real samples produced by SLM and analysed by the electron backscatter diffraction (EBSD) method. The comparison shows similarities of EBSD and CMD sample patterns and evidences for the capability of the large-scale atomistic simulations to reproduce main features of the microstructures formed in the metallic SLM additive production.

Microscopic mechanisms of the crystallization from the melt provide for conversion of short-range order of a liquid state into the long-range order of a solid crystalline state and determine in much the primary microstructure. The ”choice” of proper crystalline structure is not a trivial process that is ruled by thermodynamics. On the other hand from the microscopic point of view it takes time for atoms to be incorporated into ordered structure that leads to formation of some intermediate region between disordered liquid and crystal. In the paper the origin and properties of the region that was called ”the pre–crystallization layer” are investigated within atomistic simulation approach by the classical molecular dynamics. The simulations were carried out for model Fe–Ni–Cr alloy that is crystallized into face centered cubic lattice. It was shown that the properties of the pre–crystallization layer are different from those of liquid and solid. Its structural peculiarities lead to formation of primary defects of just solidified material crystal structure and depend on the orientation of solidification front relative to the crystal lattice.

Designing the chemical composition of new heat-resistant materials, including a new group of cobalt-based materials strengthened with the L1 2 phase with the general formula Co 3 (Al,X), requires the introduction of numerous alloy components, stabilizing the strengthening phase into the base composition. Typically, these are elements of high melting metals, whose main role is to stabilize the interphase boundary between the matrix and L1 2 precipitates and, in some way, strengthen the solid solution. These elements are characterized by high bond energy. On the other hand, the high content of this type of alloy addition increases the tendency of the alloy to release undesirable topologically compact phases, which rapidly deteriorate the mechanical properties of the alloy. These phases usually form in interdendritic areas, generating the so-called melting onset temperature, which deviates significantly from the solidus value. Therefore, the ability to predict the type and number of topologically compact phases being formed allows for the skilful design of the chemical composition of the alloy and its heat treatment, ensuring full dissolution of the mentioned phases in the matrix. This topic is the area of research in this article and concerns the Co–20Ni–9Al–7W–3Re–2Ti alloy in its immediately as-cast state. The scope of the research included simulations using the CALPHAD method and prediction of the phase composition of precipitates using two-dimensional structure maps. The obtained theoretical results were verified in microstructural tests using the STEM method and correlated with the results of DTA tests.

The study investigated the primary structure of the new generation of superalloys based on Co-10Al-5Mo-2Nb and Co-20Ni- 10Al-5Mo-2Nb cobalt. Research on a group of cobalt-based materials was initiated in 2006 by J. Sato [1]. These materials may replace nickel-based superalloys in the future due to their excellent properties at elevated temperatures relative to nickel-based superalloys. The primary microstructure characterisation of the Co-10Al-5Mo-2Nb and Co-20Ni-10Al-5Mo-2Nb alloy are the basic subject of this article. The Co-10Al-5Mo-2Nb and Co-20Ni-10Al-5Mo-2Nb alloy are tungsten free alloys of a new type with the final microstructure based on the Co-based solid solution L12 phase of the Co3(Al,Mo,Nb) type as a strengthened structural element. The analysed alloys were investigated in an as-cast state after a vacuum casting process applied on graphite moulds. The primary microstructure of the alloys and the chemical constituent of dendritic and interdendritic areas were analysed using light, scanning electron and transmission microscopy. Currently, nickel-strengthened γ’ phase steels are still unrivalled in aerospace applications, however, cobalt based superalloys are a response to their existing limitations, which do not allow maintaining the current rate of development of aircraft engines.

The characterization of the primary microstructure of the new Co-based superalloy of Co-20Ni-9Al-7W-3Re-2Ti type was shown in this article. The investigated alloy was manufactured by induction melting process from pure feedstock materials. The fundamental technological problem related to Co-Al-W-X multicomponent alloys casting process is a strong susceptibility to interdendritic segregation of alloying elements, especially tungsten and rhenium. The performed analysis revealed that the observed effect of alloying elements segregation was detectable and much stronger than for Co-9Al-9W and Co-20Ni-7Al-7W alloys, related to titanium, nickel, and aluminium migration to inter-dendritic spaces. Consequently, the tungsten concentration gradient between dendritic and interdendritic zones was higher than for Co-9Al-9W and Co- 20Ni-7Al-7W alloys. The same situation was in the case of rhenium and cobalt, but Co concentration in the interdendritic zone was only slightly lower.

The primary microstructure of new Co-based superalloy of Co-20Ni-7Al-7W (at.%) type was showed in this article. The alloy was manufactured by induction melting in vacuum furnaces. This alloy is a part of new group of high-temperature materials based on Co solid solution and strengthened by coherent L12 phase similar to Ni-based superalloys with γʹ phase. The final form of Coss/L12 microstructure is obtained after fully heat treatment included homogenization, solutionizing and aging processes. But first step of heat treatment thermal parameters determination is characterization of primary microstructure of alloys after casting process with special attentions on segregations of alloying elements in solid solution and presences of structural elements such as eutectic areas, and other phases precipitations. In analysed case the relatively high homogeneity of chemical composition was expected especially in the case of W distribution, what was confirmed be SEM/EDS analysis in dendritic and interdendritic areas.

The nuclear reactor pressure vessel is an important component of a nuclear power plant. It has been used in harsh environments such as high temperature, high pressure, neutron irradiation, thermal aging, corrosion and fatigue for a long time, which puts forward higher standards for the performance requirements for nuclear pressure vessel steel. Based on the characteristics of large size and wall thickness of the nuclear pressure vessel, combined with its performance requirements, this work studies the problems of forging technology, mechanical properties, irradiation damage, corrosion failure, thermal aging behavior and fatigue properties, and summarizes the research progress of nuclear pressure vessel materials. The influencing factors of microstructures evolution and mechanism of mechanical properties change of nuclear pressure vessel steel are analyzed in this work. The mechanical properties before and after irradiation are compared, and the influence mechanisms of irradiation hardening and embrittlement are also summarized. Although the stainless steel will be surfacing on the inner wall of nuclear pressure vessel to prevent corrosion, long-term operation may cause aging or deterioration of stainless steel, resulting in corrosion caused by the contact between the primary circuit water environment and the nuclear pressure vessel steel. Therefore, the corrosion behavior of nuclear pressure vessels materials is also summarized in detail. Meanwhile, the evolution mechanism of the microstructure of nuclear pressure vessel materials under thermal aging conditions is analyzed, and the mechanisms affecting the mechanical properties are also described. In addition, the influence mechanisms of internal and external factors on the fatigue properties, fatigue crack initiation and fatigue crack propagation of nuclear pressure vessel steel are analyzed in detail from different perspectives. Finally, the development direction and further research contents of nuclear pressure vessel materials are prospected in order to improve the service life and ensure safe service in harsh environment.

In this paper, the effects of cooling conditions on the solidification microstructure and mechanical properties of Al–18Si alloy were studied. Results show that the cooling rate up to about 250 K/s could be obtained with an ultra-low temperature copper tube in the process of melt rapid cooling + mold cooling, which could completely inhibit the precipitation of primary silicon and promote the formation of pseudo-eutectic structure in Al–18Si alloy. While in the existing research, the cooling rate was in the range of 150–200 K/s, which could only refine the primary silicon in the solidification microstructure of hypereutectic Al–Si alloys. With the change of cooling conditions, eutectic silicon changes from needle sheet with large lamellar spacing to fine sheet and then, too dense rod-like structure. The α-Al phase is transformed into a fine dendrite. The impact toughness, tensile strength, and elongation of melt rapid cooling + mold cooling Al–18Si alloy are 29.2 J/cm 2 , 241 MPa, and 6.4%, respectively. Melt rapid cooling + mold cooling is an effective method to inhibit the precipitation of primary silicon in hypereutectic Al–Si alloys.

SummaryThis study evaluated bone features of PHPT using HR-pQCT. The results showed both cortical and trabecular bones were significantly impaired in PHPT patients. Male and female PHPT patients suffered similar damages in bone. HR-pQCT indices were not observed to differ in MEN1 and sporadic PHPT patients.IntroductionHigh-resolution peripheral quantitative CT is a novel imaging technique used to separately assess trabecular and cortical bone status of the radius and tibia in vivo. Using HR-pQCT, we aimed to evaluate bone features of primary hyperparathyroidism patients in a Chinese population and reveal similarities and differences in bone features in multiple endocrine neoplasia type 1–related PHPT and sporadic PHPT patients in the Chinese population.MethodsA case-control study was designed. In 58 PHPT patients and 58 sex- and age-matched healthy controls, the distal radius and tibia were scanned using HR-pQCT. Areal bone mineral density (aBMD) was also determined in PHPT patients using dual-energy X-ray absorptiometry (DXA).ResultsIn comparison with controls, PHPT patients were observed to exhibit reduced volumetric BMD at the cortical and trabecular compartments, thinner cortices, and more widely spaced trabeculae. Significant differences were still observed when comparing data of female and male patients with age-matched controls separately. MHPT patients (n = 11) were found to have lower aBMD Z-scores in the lumbar spine, trochanteric region, and total hip compared with sporadic PHPT patients (n = 47), while no differences were observed in HR-pQCT indices between the two groups. In multiple linear regression models, no significant correlations were identified between PTH and HR-pQCT indices. However, height was found to positively correlate with HR-pQCT-derived trabecular indices at both the radius and tibia.ConclusionsPHPT affects geometry, volumetric density, and microstructure in both the cortical and trabecular bones in both male and female Chinese patients. MHPT patients were observed to have reduced aBMD as determined by DXA in the lumbar spine and hip in comparison with sporadic PHPT patients. However, HR-pQCT indices were not observed to differ.

Transport and fate of particulate organic carbon (POC) and nutrients through marine particles co-determine the future response of ocean biogeochemistry and oceanic carbon uptake under climate warming. This makes the parametrization of the biological carbon pump in Earth system models (ESMs) an important model component and motivates us to compare the recently developed, particle composition-dependent sinking scheme (M4AGO; Maerz et al., 2020) to the current CMIP6 default Martin curve-like sinking scheme in MPI-ESM1.2-LR (see Mauritsen et al., 2019) under the future shared socio-economic pathway high-emission scenario SSP5-8.5. In their global response, the two model versions are similar, showing a decrease of integrated net primary production between the historical (1985–2014) and future (2070–2099) period of about 8.1 % and 9.7 % for the CMIP6 and M4AGO version, respectively. However, the models response differs latitudinally. In M4AGO, the temperature-dependent remineralization offsets the future increase in sinking velocity caused by a higher CaCO3 to POC ratio in the low latitudes. There, M4AGO thus buffers the export loss of nutrients to the mesopelagic, visible in little future changes of the export to net primary production ratio (the peg ratio), while the CMIP6 version shows more pronounced changes with regionally declining or increasing peg ratio. In the Arctic Ocean, the projected future increase of net primary production in the CMIP6 version is diminished with M4AGO through its higher POC transfer efficiency in high latitude regions. Hence, the more mechanistic and to environmental changes-responding M4AGO scheme shows a stronger buffering regional response to climate warming than the CMIP6 model version. The higher transfer efficiency leads to enhanced CO2 uptake in high latitude regions while the tropical regions turn later into a net sink with M4AGO compared to the standard CMIP6 version. Next to ballasting, we identified the particle microstructure as vigorous determinant for future changes of POC sinking velocity. Microstructure co-determines particle porosity and particle density. Processes governing the microstructure thus can be regarded as decisive to understand for reducing uncertainty of future POC fluxes.