Titanium Zirconium Molybdenum Research Articles

Cleaning of two mirrors in first mirror unit using radio frequency capacitively coupled plasma

Abstract The first mirror (FM) cleaning, using radio frequency plasma, has been proposed to recover the FM reflectivity in nuclear fusion reactors such as ITER. To investigate the influence of simultaneous cleaning of two mirrors on mirror cleaning efficiency and uniformity, experiments involving single-mirror cleaning and dual-mirror cleaning were conducted using radio frequency (RF) capacitively coupled plasma in the laboratory. For the test and simultaneous cleaning of two mirrors, the FM and second mirror (SM), both measuring 110 × 80 mm2, were placed inside the first mirror unit (FMU). They were composed of 16 mirror samples with a dimension of 27.5 × 20 mm2 each. These mirror samples consist of a titanium-zirconium-molybdenum (TZM) alloy substrate, a 500 nm molybdenum intermediate layer, and a 30 nm aluminum oxide (Al2O3) surface coating as a proxy for Be impurities. The cleaning of a single first mirror (SFM) and the simultaneous cleaning of FM and SM (DFM and DSM) were lasted for 9 h using argon (Ar) plasma at a pressure of 1 Pa. The total reflectivity of mirror samples on the DSM did not fully recover and varied with locations with a self-bias of −140 V. While with a self-bias of −300 V, the total reflectivity of mirror samples on SFM and DFM was fully recovered. The energy dispersive spectrometer (EDS) results demonstrated that the Al2O3 coating had been completely removed from these mirror samples. However, the mass loss of each mirror sample on SFM and DFM before and after cleaning varied depending on their locations, with higher mass loss observed for mirror samples located in the corners and lower for those in the center. Compared to the single mirror cleaning, the simultaneous cleaning of two mirrors reduced the difference of the mass loss between the highest and lowest. Furthermore, this mass loss for the mirror samples of DFM facing the DSM was increased. It indicated that the simultaneous cleaning of mirror samples face to face in the FMU could influence each other, highlighting the necessity for special attention in future studies.

Numerical analysis of the powder mixed electrical discharge machining (PMEDM) process for TZM-molybdenum superalloy using finite element method

The powder mixed electrical discharge machining (PMEDM) process was simulated via finite element analysis in the current study to assess heat behavior and material removal rate. The goal of this paper is to conduct a thorough experimental and thermal examination of electrical discharge machining (EDM) in order to forecast its cutting characteristics and subsequently optimize the output variables using a response surface methodology for simulations and choosing the most suitable set of process variables related to the PMEDM process. This study’s objective is to design a 2D axisymmetrical transient thermal model that might also describe the physics of material removal in a single spark PMEDM operation on a Titanium Zirconium Molybdenum (TZM) superalloy. ANSYS (version 9.1) software is used to perform transient heat transfer simulations to determine the temperature profile with the amount of material removal at different current, pulse on and off times, gap voltages, and fraction of heat that enters the specimen. The PMEDM process produced craters with a lower diameter and depth, which increased the material removal rate and enhanced the surfacing quality. Compared to the conventional EDM process, the inclusion of powder raised the heat flux given to the work material by 10%–12%. It has been determined that with the single spark modeling technique, the temperature significantly dropped in both the radial and depth directions. The computational results are compared with experimental observations for similar machining conditions, and both results agree satisfactorily.

Laser Powder Bed Fusion Additive Manufacturing of Mo and TZM Exoskeleton with Cu Infiltration for New Heat Sinks Configuration

This study reports the fabrication and characterization of molybdenum (Mo) metal and titanium‐zirconium‐molybdenum (TZM) alloy exoskeletons with honeycomb cavity structures (HCS) that are infiltrated with oxygen‐free high conductivity (OFHC) Cu under an inert atmosphere as a potential replacement for Cu‐Mo‐Cu laminate in heat sink applications for power electronics semiconductors like GaAs. The thermal expansion behavior and the thermal loading of the starting Mo and TZM structures, and of the Cu‐infiltrated parts are evaluated. The fabricated Mo and TZM structures with density >99% and Mo‐based heat sinks with improved CTE (6.6 × 10−6 K−1) when compared to conventional Cu‐Mo‐Cu laminated heat sinks (CTE = 7.6 × 10−6 K−1). The new Mo and TZM structures promise superior performance due to their closer CTE to that of GaAs and similar semiconductors (CTE = 5.7 × 10−6 K−1). Exposure to temperatures up to 1073 K did not affect the Mo microstructure due to the inherent resistance to recrystallization, while exposure to 1373 K did reduce hardness. In contrast, TZM exoskeletons showed resistance to recrystallization even at 1373 K. The fabricated composite heat sinks showed thermal diffusivity (≈61 × 106 m2 s−1) that is within the upper limits of those reported for commercial laminated heat sinks (45 to 65 × 106 m2 s−1).

Taguchi optimizations on friction stir welding of nitinol alloy

The welding strength plays a vital role in all manufacturing sectors in welding proces. At the same time, advanced materials with reinforced particles offers good welding strength. The admirable weldability characteristics are attained by friction stir welding process (FSW). Cubic Boron Nitride - CBN, Titanium Zirconium Molybdenum - TZM acts as a tool material in FSW process which gives good welding strength when compared to other tool material. Silicon carbide based nitinol composite is manufactured by stir casting route which provides admirable substance properties. Scanning Electron Microscope (SEM) was used to analyze the material characteristics. The welding strength obtained from two tool materials were compared. The optimal strength of the joint is attained by Taguchi optimization. The objective of the research work is to increase the welding strength using TZM tool. Optimal strength of welding was obtained at rotational speed of tool: 1499.9 rpm, speed of welding at 49.9 mm/min, feed: 9.9 mm/min.

Effect of Ti[sbnd]Cr filler on microstructure, mechanical properties, and thermal shock resistance of TZM/graphite brazed joints

The objective of this work was to braze titanium zirconium molybdenum(TZM) alloy and graphite with Ti40Cr filler in order to explore its practical application on computed tomography tube target. The brazed joints' microstructure, mechanical properties, and thermal shock properties were characterized by X-ray diffraction, scanning electron microscopy, and a 3D laser confocal measuring microscope. The results indicated that the interface microstructure of TZM/graphite brazed joints was graphite/Cr3C2/TiC/Ti-Cr(Mo)/Ti-Mo(Cr)/TZM, and the thickness of the brazing seam increases with increasing temperature. In contrast, the thickness of the carbide reaction layer near the graphite side gradually becomes thicker. The shear tests showed that the joint's strength increased with the temperature increase in a specific temperature range. Maximum shear strength of 26.5 MPa was reached when the joint with groove structure brazed at 1480 °C. The effect of holding time on the joints was similar to that of temperature, but the thickness of the carbide reaction layer did not change with holding time. The optimal brazing process for TZM/Ti-40Cr/graphite brazed joints was to hold for 20 min at 1480 °C. TZM/Ti-40Cr/graphite brazed joints were subjected to a laser thermal shock test. The results indicated that TZM/Ti-40Cr/ graphite brazed joints would not cause serious damage when subjected to 20A laser beam current. When the current rose to 40A, the joints will be broken down by the laser, and the damage depth reached −254.824 μm.

The effect of secondary phase on corrosion behaviors of the titanium–zirconium–molybdenum alloy

The effect of secondary phase on corrosion behaviors of the titanium–zirconium–molybdenum alloy

Damages of TZM as plasma facing material under transient heat load

Titanium-Zirconium-Molybdenum (TZM) is applied as the first wall material of EAST due to its excellent performance. To investigate the service behavior of TZM under transient heat fluxes, the postmortem inspection of in-situ damaged TZM tiles by plasma disruption heat load in EAST was analyzed. Meanwhile, the EMS-60 electron gun has been also used to test the transient heat load behaviors of TZM. There are some similar characteristics between the in-situ melting TZM and the ex-situ melting TZM tiles, but there are also some obvious differences. Specifically, in some melting zone, the surface morphology of partial in-situ TZM melting region is like that of ex-situ TZM melting areas, and their convex surface is relatively smooth, while the concave surface is relatively rough, and the solidification layer undergoes recrystallization. In other melting areas, there are many small pits on the surface of the TZM tile that was melted in-situ, but there are no obvious pits on the surface of the ex-situ TZM sample, and part of the surface of the TZM tile that was melted in-situ is like a big pit, and the melted TZM droplets in this melting area tend to splash towards the periphery. The capillary waves around the castle structure in the ex-situ test samples are the result of wetting effect of liquid metal and capillary force, and the holes in the resolidified layer is caused by the overheating boiling of TZM liquid. On the other hand, the number and propagation direction of cracks in the in-situ TZM tile are more complex than those in the ex-situ TZM sample. Firstly, the number of cracks on the in-situ TZM tile is large and dense, while the number of cracks on the surface of the ex-situ melting sample is small and scattered. The crack width of the in-situ tile is greater than that of the ex-situ tile. Secondly, the crack extension direction on the in-situ melted TZM is diverse, while the extension direction of the surface crack on the ex-situ TZM sample is relatively simple, and there is only one kind of crack on the tile surface. Such results provide reference for understanding the thermal behavior of TZM under transient heat flux in fusion devices.

Effect of Al content on 1200 °C steam oxidation behavior of Cr-based coatings on TZM alloy

In this paper, the 1200 °C high temperature steam oxidation behavior of Cr-based coatings with different Al content (0, 15 at%, 30 at%, 50 at%) deposited on titanium-zirconium-molybdenum (TZM) alloy has been investigated. The oxidation resistance of TZM alloy is significantly increased by the Cr-based coatings. The Cr70Al30 coating exhibits the best performance due the protectiveness of a triple oxide layer formed on coating surface, including outer Al2O3 and Cr2O3 mixed layer, intermediate Cr-rich oxide (Cr2O3) layer and inner Al-rich oxide (Al2O3) layer. The effect of Al content on the oxidation resistance of Cr-based coatings is discussed in detail.

Machine learning approach to model and predict the shear strength of TZM-graphite joint bonded by spark plasma sintering

These days, the study of titanium alloys has grown into a sizable topic of study. Due to its remarkable high-temperature applications, titanium zirconium molybdenum (TZM) is one such alloy with considerable research potential. In this study, the shear strength of TZM-graphite alloy, which was bonded using the spark plasma sintering (SPS) process with titanium foil as an interlayer, has been predicted using a machine learning approach. The shear strength of the TZM-graphite alloy depends on various process parameters such as sintering temperature, sintering pressure, holding time, and intermediate layer thickness. Since the correlation between input variables and output variables is intricate and non-linear, an artificial neural network (ANN) model was developed in this research to investigate the relationship between bonding parameters and the shear strength of the TZM-graphite joint. The feed-forward backpropagation neural network was utilized for training the model and predicting the shear strength. By computing the Mean square error (MSE) and Average error (AE), the optimum number of neurons in the hidden layers was determined. Consequently, the model with 4–9-9–1 architecture was constructed, and its accuracy was assessed by contrasting the values obtained by the neural network with actual experimental data. The model was then validated using a variety of performance measuring indicators such as mean absolute percentage error (MAPE) and root mean square error (RMSE). The achieved correlation coefficient (R-value) of 0.99614% demonstrates that the proposed ANN model is an excellent fit for the experimental data to predict the accurate shear strength of the TZM-graphite joint. For further understanding of the influence of input parameters on the shear strength of the TZM-graphite joint, 2D and 3D surface graphs were plotted.

Commissioning and first results of the OLMAT facility

The OLMAT (Optimization of Liquid Metal Advanced Targets) facility has recently undergone the commissioning and start-up phases. Solid Titanium-Zirconium- Molybdenum (TZM) alloy and liquid tin (Sn) metallic targets were exposed to a hydrogen neutral beam injector (NBI) particle flux with power densities up to 58 ± 14 MW/m2, pulse duration up to 150 ms, and repetition rates up to 2 pulses/minute. These beam parameters are well above the estimates based on the typical performance of this NBI system when used for heating plasmas in the TJ-II stellarator. The parameters of the plasma generated through the interaction of the fast (32.5 keV) neutrals and ions and the solid were characterized by spectroscopic methods while surface temperature and total absorbed power were followed using pyrometry, infrared (IR) thermography, and calorimetry, respectively. Targets were visually monitored during the exposure and microscopically analyzed ex-situ. Electrical isolation of the target permitted recording the floating voltage during irradiation as well as for active biasing tests. In this work, a description of the facility, its operating parameters, and firsts results are provided and assessed as a new High Heat Flux (HHF) Facility for testing solid and liquid metal divertor targets under reactor-relevant heat load conditions.

Material Plasma Exposure eXperiment (MPEX) High Heat Flux Bellows for Component Alignment in High Microwave Environment

The Material Plasma Exposure eXperiment (MPEX) device is a linear plasma device developed to perform plasma material interaction experiments under the conditions prototypic of a fusion reactor divertor. MPEX has multiple systems that must be precisely aligned to the plasma axis, including an electron cyclotron heating system that emits up to 400 kW of microwave power into the vacuum vessel. Five distinct systems require precise alignment on the MPEX device, thus requiring four bellows, all of which are adjacent to the plasma at a relatively high heat flux of approximately 47 kW/m2 and microwave power regions. The MPEX high heat flux bellows (HHFB) is designed to deliver 6 degrees of freedom positioning. The HHFB includes titanium–zirconium–molybdenum (TZM) inserts that are brazed into a Glidcop AL-15 body using a high-temperature braze alloy, thus blocking direct line of sight to an edge-welded bellows from the plasma and microwave screen to block microwaves from the bellows. A custom ConFlat knife edge is machined into the Glidcop AL-15, so the vacuum flanges do not need a braze or weld joint on the vacuum interface. Fingerstock or copper mesh is used to restrict microwave power from entering the interstitial space between the water-cooled Glidcop AL-15 body and edge-welded bellows. Glidcop AL-15 was selected as the material of choice for the water-cooled body because it can maintain mechanical integrity at elevated temperatures, and it also allows for a high-temperature braze. TZM was selected for its machinability and compatibility with vacuum and plasma requirements. A test article is also being considered for a similarly shaped component, the MPEX limiter, that will demonstrate the integrity of the braze joint under high thermal load. Results from this testing will be extrapolated to deduce the lifetime and integrity of the HHFB design.

MPEX High Heat Flux Plasma Dump Design, Manufacture, and Articles Test

The Material Plasma Exposure eXperiment (MPEX) device is a steady-state linear plasma device currently in the final design phase at the Oak Ridge National Laboratory. This device will reach ion fluences up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{31}\,\,\text{m}^{-2}$ </tex-math></inline-formula> and will be used to expose neutron-irradiated materials to divertor-relevant plasmas and to study the effects of plasma-material interactions. These studies will elucidate the complex effects of plasmas with divertor candidate materials capable of withstanding high heat flux and high fluences for next-generation fusion devices. Bidirectional plasma will be generated using a high-power (200 kW) helicon source. Plasma will be confined by superconducting magnets. The last plasma-facing component on the upstream side of the MPEX device is the dump, which has been designed to intercept plasma and energetic particles. The dump will have a total heat load of 9.2 kW. A copper alloy (Glidcop AL-15) was selected for use in the water-cooled flange design because of its high thermal conductivity, its retaining strength at elevated temperatures, and its ability to be used in the high-temperature braze joints used in this application. Titanium-zirconium-molybdenum (TZM) tiles are brazed to the Glidcop AL-15 flange using high-temperature braze alloy. External water-cooling channels are used on the dump flange to prevent water leakage inside the vacuum space. This article discusses the details of the high heat flux dump design, including the computational fluid dynamics (CFD) and structural analyses performed to validate the design to meet the operational requirements of the MPEX device.

Investigation of microstructures, defects, and mechanical properties of titanium-zirconium-molybdenum alloy manufactured by wire arc additive manufacturing

Titanium‑zirconium‑molybdenum (TZM), one of the refractory alloys, has extraordinary physicochemical properties, making it ideal for usage in extreme environmental applications (e.g., high-temperature and nuclear). Due to the scalability and near-net shape fabrication, metal additive manufacturing processes have several advantages, leading it to be the possible solution for the fabrication of refractory alloy structures. Wire arc additive manufacturing (WAAM) has several advantages, including high deposition rate, energy efficiency, and cost-effective manufacturing of large components. In this study, we comprehensively investigated the relationships among process, microstructures, mechanical properties, and defects of TZM thin-walls manufactured by WAAM using four heat input conditions: 180A, 200A, 220A, and 240A. The microstructures were investigated using multi-scale material characterization techniques. Columnar grains were generated along the build direction, and carbide precipitates were found uniformly distributed in the Mo matrix. Multi-scale pores and cracks were present in the microstructures. The average microhardness values for the deposits ranged from 188.5 to 193.5 hardness scales of Vickers. The highest yield strength, 195 MPa, was found in the 200A heat input condition. The primary fracture mode was identified as a brittle transgranular. The area fraction of porosity was calculated >1% in each condition, with the largest being 2.04% in the 240A deposit.

Strain hardening behaviour of friction stir welded magnesium alloy

The present investigation is used to analyze the strain hardening behaviour of friction stir welded magnesium alloy. Hot rolling process is involved in strain hardening of magnesium alloy. The alloy is operated at above the recrystallization temperature. Titanium zirconium molybdenum (TZM) and cubic boron nitride (CBN) tool tip is considered for friction stir welding process (FSW). Vicker hardness tester is used to evaluate the hardness after strain hardening process. In FSW process, tool rotational speed, welding speed and feed is considered to evaluate the hardness. Hardness is measured and compared with tool tip materials. The optimal hardness is attained by taguchi method. Surface plot is used to analyze the correlation between input and output constrains. Liquid penetrant inspection is utilized to found the defects in welded joints. Optimal hardness was achieved at tool rotational speed of 1500 rpm, welding speed of 50 mm/min and feed of 15 mm/min.

Optimization of welding strength on zirconium plate

The present investigation is used to evaluate the friction stir welding strength in zirconium plate. The good quality welding strength has got by using friction stir welding (FSW) process along with Titanium Zirconium Molybdenum (TZM) tool tip. TZM toll tip has come along with scroll bottom end. It is used to enhance the tool life and welding strength. The welding strength is measured by Cubic Boron Nitride (CBN) and TZM. Tool speed, feed and welding speed was used to measure the welding strength. For every FSW process, the important parameters are created by the method of Analysis of variance (ANOVA) as well as mathematical models have been calculated for the hardness of welding joints. Taguchi method has been used to analyze machining parameters and optimal welding. The most favorable welding strength was attained at tool rotational speed of 1500 rpm, welding speed of 50 mm/min and feed of 10 mm/min. Tool rotational speed (86.82 %) was played an essential role in welding strength.

Properties of Titanium Zirconium Molybdenum Alloy after Exposure to Indium at Elevated Temperatures.

Titanium zirconium molybdenum (TZM) is a high strength at high temperature alloy with favorable properties for use in high temperature structural applications. Use of TZM in high pressure, gas-containing autoclave systems was recently demonstrated for the ammonothermal method. Use of indium (In) in the system is desired, though there is a general lack of literature and understanding on the corrosion and impact of In on the mechanical properties of TZM. This study reports for the first time the mechanical properties of TZM after exposure to metallic In at temperatures up to 1000 °C. Static corrosion testing of TZM in In were performed at 750 °C and 1000 °C for 14 days. A microstructure analysis was performed suggesting no visible alteration of the grain structure. Differential thermal analysis (DTA) was performed to investigate compound formation between In and the primary constituents of TZM yielding no measurable reactions and hence no noticeable compound formation. X-ray energy dispersive spectroscopy (EDS) line scans across the TZM-In interface revealed no measurable mass transport of In into the TZM matrix. These results were confirmed using X-ray diffraction (XRD). Given the apparent inertness of TZM to In, mechanical properties of TZM after exposure to In were measured at test temperatures ranging from 22 °C to 800 °C and compared to unexposed, reference TZM samples from the same material stock. Tensile properties, including ultimate tensile strength, yield strength and total elongation, were found to be comparable between In-exposed and unexposed TZM samples. Impact fracture toughness testing (Charpy) performed at temperatures ranging from −196 °C to 800 °C showed that TZM is unaffected upon exposure to In. Tensile testing indicated ductile behavior at room temperature (slow strain rate) whereas impact testing (high strain rate) suggested a ductile to brittle transition temperature between 100 °C and 400 °C. Given these results, TZM appears to be a promising candidate for use as a force bearing material when exposed to In at high temperature.

Brazing characteristics, microstructure, and wettability of laser powder bed fusion additive manufactured GRCop-84 compared to CuCrZr and OFC, and brazing to titanium-zirconium-molybdenum alloy limiters

Laser Powder Bed Fusion (L-PBF) of Glenn Research Copper 84 (GRCop-84), a Cr2Nb (8 at. % Cr, 4 at. % Nb) precipitation hardened alloy, produces a fully dense, high conductivity alloy with a yield strength of 500 MPa and ultimate tensile strength (UTS) of 740 MPa with 20% elongation; superior to other competing copper alloys. Braze wetting characteristics of GRCop-84 with Ag-Cu-X, and Au-Cu brazes were similar to CuCrZr, but less than oxygen free copper. No difference in wetting was observed between infill and surface contour areas in L-PBF GRCop-84. Wet sanding to 240 grit (Ra=0.24 µm) was considered the optimal surface condition. Silver diffusing through GRCop-84 depleted Cr2Nb precipitates from the copper grain and deposited agglomerations of coarsened precipitates within silver-rich regions of intergranular diffusion once a density threshold was reached. Microstructure modification was minimized with 50Au-50Cu braze implying that silver caused precipitate coarsening and agglomeration, and not high temperature exposure. Coarsened precipitates were observed on the surface within braze pools implying a contribution to braze wetting. Palcusil-25, Ticusil, CuSil-ABA, and 50Au-50Cu brazes were suitable for brazing to unplated Titanium-Zirconium-Molybdenum (TZM), while sulfamate nickel plating to allows wetting with CuSil or other non-active brazes. Vacuum brazing techniques were developed to join a 1 mm thick layer of TZM to the front of additive manufactured GRCop-84 waveguides considering the brazing characteristics of both GRCop-84, TZM, and internal stress from the difference in coefficient in thermal expansion.

The formation mechanism of micro-nano secondary phase in solid-liquid doped TZM alloy

Among the various secondary phases distributed in the TZM (Titanium-Zirconium-Molybdenum) alloy matrix, the ones that can play a strengthening role are often those with a particle size smaller than 1 μm. In this study, titanium sulfate, zirconium nitrate, and fructose were used as raw materials. The TZM alloy with uniform distribution and an average secondary phase particle size of 940 nm (hereinafter referred to as MN-TZM alloy) was prepared through a solid-liquid doping preparation process. The thermodynamic calculation reveals the formation mechanism of the micro-nano-level secondary phase in the MN-TZM alloy. Thermogravimetric analysis (TG-DSC, TG-MS) and transmission electron microscope (TEM) confirmed the calculation results. The generation process of the micro-nano secondary phase evolution can be divided into four parts. The first stage is the process of solute dissolution at room temperature. In the second stage, doping and drying process take place below 100 °C. Third, reduction and secondary phase precursor incubation processes occur from 100 to 700 °C. Fructose decomposes (100 °C) to obtain organic carbon and water. The decomposition of zirconium nitrate (100 °C) yields NH 3 , H 2 O, ZrO 2 and Zr, while the titanium sulfate decomposes directly at 200– 242 °C to obtain SO 2 , H 2 O, TiO 2 and Ti. In the last stage, the secondary phase nucleates and grows up (700– 1800 °C). A large variety of micro-nano-scale and even nano-scale secondary phase particles have been discovered, including TiO 2 , ZrO 2 , ZrC and TiC. These observations provide necessary information for tracing back the secondary phase precipitation mechanism in the manufacturing process of high-performance molybdenum alloys. • The average grain size of MN-TZM alloy is 940 nm. • The micro-nano secondary phase reduces the average grain size of TZM alloy by 26%. • TZM alloy was prepared from titanium sulfate, zirconium nitrate, fructose and molybdenum powder for the first time. • The formation mechanism of micro-nano secondary phase in TZM alloy was clarified.

Conceptual design and thermal-hydraulic analysis of a megawatt-level lead-bismuth cooling reactor for deep-sea exploration

A new conceptual design of a mega-power nuclear reactor (MPNR) for applications in deep-sea exploration was developed. A solid core cooled by the natural circulation of a lead-bismuth eutectic (LBE) reactor was designed with a thermal power of 1 MW. It consists of 126 coolant channels, which are holes surrounded by highly enriched fuel of UO2 dispersed in titanium-zirconium-molybdenum (TZM) alloy. A control rod at the center of the fuel and six control drums around the block are made of boron carbide to control the reactivity of the reactor. The core and heat exchangers are arranged horizontally to reduce the volume of the entire system. Compared with traditional deep-submersible reactors used at sea, the MPNR is highly compact, has a high-power output and simple structure, and ensures safety under ocean conditions. The neutronic and thermal-hydraulic design characteristics of the MPNR were calculated and assessed. The temperature reactivity and void fraction reactivity coefficients of the MPNR are negative values to ensure that the reactor has negative feedback characteristics. The thermal-hydraulic analysis of the MPNR design was carried out using the computational fluid dynamics program STAR-CCM+, in which field functions were added to the program to realize the inclined, rolling, and heaving motions of the reactor. The numerical simulations showed that under stationary conditions, the MPNR could establish natural circulation with a mass flow rate of 93.32 kg/s. At an inclination angle of ±30°, the natural circulation mass flow rates are 88.6 kg/s and 87.5 kg/s, respectively. Under rolling and heaving conditions, the mass flow rate fluctuated periodically, and the maximum temperature of the core changed within 10 K.

Precise control of oxygen for titanium-zirconium-molybdenum alloy

Organic carbon has been used as a reducing agent to reduce the oxygen content in the TZM (Titanium-Zirconium-Molybdenum) alloys for the first time. The TZM alloys were prepared by the powder metallurgy sintered by hydrogen and vacuum, respectively. With increasing the organic carbon content from 0.04 wt% to 0.8 wt%, the influence of organic carbon content and sintering methods on the oxygen content of TZM alloys and their action mechanism were studied. The results show that the oxygen content of TZM alloy sintered by hydrogen decreases significantly with the increase of organic carbon. The oxygen content is as low as 300 ppm when the organic carbon is 0.8 wt%. The oxygen content of the TZM alloy varies between 50 ppm and 110 ppm under vacuum sintering. When the oxygen content decreases, the secondary phase particles precipitated in the alloy decrease the alloy's hardness due to the weakening effect of solution strengthening and secondary phase strengthening. The density of TZM alloy decreases with increasing organic carbon, whether in vacuum or hydrogen sintering. Verification experiments confirm the accuracy of the conclusion. As the oxygen content decreases from more than 3000 ppm to less than 1000 ppm, the secondary phase particles in the TZM alloy changed from mostly TiO2 and ZrO2 to Ti/Zr composite oxide particles containing zirconium-rich stripes. In the state of the lowest oxygen content, only zirconia was found in the matrix