IMPROVEMENT OF TYPE IV CRACKING RESISTANCE OF 9Cr HEAT RESISTING STEEL WELDMENT BY BORON ADDITION

Creep lives of high Cr ferritic heat resisting steel weldments decrease due to Type Ⅳ fracture, which occurs as a result of formation and growth of creep voids and cracks on grain boundaries in fine-grained heat affected zone (HAZ). Because boron is considered to suppress the coarsening of grain boundary precipitates and growth of creep voids, we have investigated the effect of boron addition on the creep properties of 9Cr steel weldments. Four kinds of 9Cr3WSCoVNb steels with boron content varying from 4.7×10-5 to 1.8×10-4 and with nitrogen as low as 2.0×10-5 were prepared. The steel plates were welded by gas tungsten arc welding and crept at 923K. It was found that the microstructures of HAZ were quite different from those of conventional high Cr steels such as P91 and P92, namely the fine-grained HAZ did not exist in the present steel weldments. Boron addition also has the effect to suppress coarsening of grain boundary carbides in HAZ during creep. As a result of these phenomena, the welded joints of present steels showed no Type Ⅳ fractures and much better creep lives than those of conventional steels.

Wire arc additive manufacturing of a heat-resistant Al-Cu-Ag-Sc alloy:microstructures and high-temperature mechanical properties

With a high energy efficiency,low geometric limitation,and low cracking susceptivity to cracks,wire arc additive manufacturing(WAAM)has become an ideal substitute for casting in the manufacturing of load-bearing high strength aluminum components in aerospace industry.Recently,in scientific researches,the room temperature mechanical performance of additive manufactured high strength aluminum alloys has been continuously broken through,and proves these alloys can achieve comparable or even higher properties than the forged counterpart.Since the aluminum components for aerospace usage experience high-low temperature cycling due to the absence of atmosphere protection,the high temperature performances of additive manufactured high strength aluminum alloys are also important.However,few research focuses on that.A special 2319Ag Sc with 0.4 wt.%Ag and 0.2 wt.%Sc addition designed for high temperature application is deposited successfully via cold metal transfer(CMT)based on WAAM.The microstructures and high temperature tensile properties are investigated.The results show that the as-deposited 2319Ag Sc alloy presents an alternate distribution of columnar grains and equiaxed grains with no significant textures.Main second phases are Al_(2)Cu and Al3Sc,while co-growth of Al_(2)Cu and bulk Al_(3)Sc is found on the grain boundary.During manufacturing,nanoscale Al_(2)Cu can precipitate out from the matrix.Ag and Mg form nano-scaleΩphase on the Al_(2)Cu precipitates.At 260℃,average yield strengths in the horizontal direction and vertical direction are 87 MPa±2 MPa,87 MPa±4 MPa,while average ultimate tensile strengths are 140 MPa±7 MPa,141 MPa±11 MPa,and average elongations are 11.0%±2.5%,13.5%±3.0%.Anisotropy in different directions is weak.

Post processing of additive manufactured Mg alloys:Current status,challenges,and opportunities

Magnesium(Mg)and its alloys are emerging as a structural material for the aerospace,automobile,and electronics industries,driven by the imperative of weight reduction.They are also drawing notable attention in the medical industries owing to their biodegradability and a lower elastic modulus comparable to bone.The ability to manufacture near-net shape products featuring intricate geometries has sparked huge interest in additive manufacturing(AM)of Mg alloys,reflecting a transformation in the manufacturing sectors.However,AM of Mg alloys presents more formidable challenges due to inherent properties,particularly susceptibility to oxidation,gas trapping,high thermal expansion coefficient,and low solidification temperature.This leads to defects such as porosity,lack of fusion,cracking,delamination,residual stresses,and inhomogeneity,ultimately influencing the mechanical,corrosion,and surface properties of AM Mg alloys.To address these issues,post-processing of AM Mg alloys are often needed to make them suitable for application.The present article reviews all post-processing techniques adapted for AM Mg alloys to date,including heat treatment,hot isostatic pressing,friction stir processing,and surface peening.The utilization of these methods within the hybrid AM process,employing interlayer post-processing,is also discussed.Optimal post-processing conditions are reported,and their influence on the microstructure,mechanical,and corrosion properties are detailed.Additionally,future prospects and research directions are proposed.

Effect of Ca Addition and Heat Treatment on the A390(S)/AM60(L) Interface Microstructure

Overcasting is a new kind of dissimilar joining technique used to produce the aluminum（solid）/magnesium（liquid） bonding bi-metallic material in this study. For the Al/Mg（A390/AM60） bi-metallic samples, the interface microstructures are the research points, which directly influence the mechanical properties. It is, therefore, of vital importance to find a method to improve the interface microstructures. This research focused on the effect of the calcium（Ca） addition in the liquid Mg alloys and the heat treatment on the A390/AM60 interface microstructures of the bi-metallic samples. The testing results showed that, with Ca addition in AM60, owing to two possible reasons, the interface microstructure and the shear strength of the A390/AM60 bi-metallic samples could be improved. The heat treatment could further improve the interface microstructure and the mechanical properties by dissolving β-Mg_（17）Al_（12） into α-Mg and destroying the Mg_2Si layer structure.

Effect of Mn Addition and Heat Treatment on the Corrosion Behaviour of Mg-Ag-Mn Alloy

The high corrosion sensitivity and the potential bio-toxicity of Mg-Ag alloys limit their wide applications for the production of implanted devices. In the present work, Mn is added into the Mg-Ag alloy to optimize its corrosion behaviour. The corrosion behaviour of Mg-Ag-Mn alloys is investigated with the underlying microstructural factors examined. The Mg-Ag alloy with 2 wt% Mn exhibits the highest corrosion resistance after post-casting heat treatment at 440 ℃. The addition of Mn results in α-Mn phase with the incorporation of Fe, which suppresses the cathodic activity of impurity Fe. Further, heat treatment of the cast alloys homogenizes the distribution of Ag and promotes the precipitation of α-Mn phase. The former removes Ag segregations as potential cathodes;the latter promotes a more uniform distribution of cathodes and, therefore, prevents localized corrosion.

Effect of heat treatment on the microstructure and mechanical properties of AZ80M magnesium alloy fabricated by wire arc additive manufacturing

To maximize the benefits of wire arc additive manufacturing(WAAM)processes,the effect of post-deposition heat treatment on the microstructure and mechanical properties of WAAM AZ80M magnesium(Mg)alloy was investigated.Three different heat treatment procedures(T4,T5 and T6)were performed.According to the results,after T4 heat treatment,the microsegregation of alloying elements was improved with the eutectic structure dissolved.Samples after T5 heat treatment inherited the net-like distribution of secondary phases similar to the as-deposited sample,where the eutectic structure covering the interdendritic regions and theβ-phase precipitated around the eutectic structure.After T6 heat treatment,the tinyβ-phases re-precipitated from the matrix and distributed in inner and outer of the grains.The hardness distribution of the samples went through T4 and T6 heat treatment was more uniform in comparison to that of T5 heat treated samples.The tensile test showed that the T6 heat treatment improved the strength and ductility,and the anisotropy between horizontal and vertical can be eliminated.Moreover,T4 treated samples exhibited highest ductility.

Microstructure and mechanical properties of laser additive manufactured novel titanium alloy after heat treatment

A novel α+β titanium alloy with multi-alloying addition was designed based on the cluster formula 12[Al-Ti_(12)](AlTi_(2))+5[Al-Ti_(14)](AlV_(1.2)Mo_(0.6)Nb_(0.2))which was derived from Ti-6Al-4V.The nominal composition of this novel alloy was determined as Ti-6.83Al-2.28V-2.14Mo-0.69Nb-6.79Zr.In this study,the novel alloy and Ti-6Al-4V alloy samples were prepared by laser additive manufacturing.The microstructure,micro-hardness,room/high temperature tensile properties of the as-deposited samples were investigated.Compared to Ti-6Al-4V,the novel alloy has much higher room and high temperature(600℃)tensile strengths,which are 1,427.5 MPa and 642.2 MPa,respectively;however,it has a much lower elongation(3.2%)at room temperature because of the finer microstructure.To improve the elongation of the novel alloy,heat treatment was used.After solution at 960℃ or 970℃ for 1 h followed by air cooling and aging at 550℃ for 4 h followed by air cooling,a unique bi-modal microstructure which contains crab-like primaryαand residual β phase is obtained,improving the compression elongation by 80.9% compared to the as-deposited samples.The novel alloy can be used as a high-temperature and high-strength candidate for laser additive manufacturing.

A review on metal additive manufacturing:modeling and application of numerical simulation for heat and mass transfer and microstructure evolution

Metal additive manufacturing technology has been widely used in prototyping,parts manufacturing and repairing.Metal additive manufacturing is a multi-scale and multi-physical coupling process with complex physical phenomena of heat and mass transfer and microstructure evolution.It is hard to directly observe the dynamic behavior and microstructure evolution of molten pool during additive manufacturing.Therefore,numerical simulation of additive manufacturing process is significant since it can efficiently and pertinently predict and analyze the physical phenomena in the process of metal additive manufacturing,and provide a reference for technological parameters selection.In this review,the research progress of numerical simulation of metal additive manufacturing is discussed.Various aspects of numerical simulation models are reviewed,including:(1)Introduction of basic control method and physical description of numerical simulation models;(2)Comparison of various heat and mass transfer models based on different physical assumptions(heat conduction model;heat flux coupling model;discrete powder particle heat flux coupling model);(3)Applications of various microstructure evolution models[phase field(PF),cellular automata(CA),and Monte Carlo(MC)].Finally,the development trend of numerical simulation of metal additive manufacturing,including the thermal-flow-solid coupling model and deep learning for numerical model,is analyzed.

Influence of Bed Temperature on Heat Shrinkage Shape Error in FDM Additive Manufacturing of the ABS-Engineering Plastic

In case of manufacturing hexahedral ABS (Acrylonitrile Butadiene Styrene) plastic components using a FDM (Fused Deposition Modeling)-based 3D printer, undesirable shape errors occur in the product due to heat shrinkage. This paper experimentally ob-served the influence of the bed temperature change on the deformed shape errors of a hexahedral specimen of 100 × 50 × 50 mm3 produced by using a 3D printer. During printing work, the head nozzle temperature was kept at 240?C and the head speed was set at 50 mm/s. The chamber was enclosed with a PC-plate. 3D printing was conducted at four different bed temperatures;50?C, 70?C, 90?C, and 110?C. After the produced specimens naturally cooled down to room temperature, their deformed shape errors were measured. As a result, the higher the bed temperature, the lower the deformed shape errors of the specimens were. However, if the bed temperature had exceeded 120?C, laminating adhesion became poor. That seems to occur because of the material phase change and can make 3D printing work very hard as a consequence. Results of this study can be helpful to set optimum bed temperature condition in FDM additive manufacturing.

ENHANCEMENT OF NUCLEATE BOILING HEAT TRANSFER WITH ADDITIVES

Based on the tests of more than ten different additives, several effective additives are found capable of improving the boiling heat transfer behavior of water pronouncedly. The mechanism of the enhancement of nucleate boiling with additives has been investigated, and the results indicate that one of the important reasons is that the nucleation sites have been increased.

GRAIN STRUCTURE CONTROL OF NICKEL－BASE SUPERALLOYS IN CASTING PROCESS： EFFECT OF MELT ADDITIONS

Grain structure, dendrite morphologies and shape of MC type carbides ina nickel-base superalloy IN 738 LC are investigated with the addition of carbides,boride, nitride and intermetallic compounds. The results show that the grain size of theingots can be refined extensively to the order of ASTM M11～12 by combination of anintermetallic compound NixAly, addition together with lowering melt homogeneoustreatment temperature during the melting and casting process. In addition, the processcould restrain the formation of script-type carbides. The new process does not changethe phase constitution, freezing characteristics and sub-structure stability. Therefore, itis considered as an effective and practical method of grain refinement for superalloys.

Effects of Chinese Herbal Additive on Immunologic Functions and Productive Performance of Dairy Cows during Heat Stress

[Objective] To study effects of Chinese herbal additive on immunologic functions and productive performance of dairy cows, [Method] A total of 20 healthy dairy cows were randomly divided into control group and experimental group. They were respectively fed a common basal diet and the basal diet containing 100 g Chinese herbal additives. The trial lasted for 49 d. [ Result] The 4% fat corrected milk yield （FCM） production, milk yield after weight correction, quantity of solid-not-fat and ash content in the experimental group were significantly higher than those in the control group （ P 〈 0.01 ）. The total lymphocytes （LYM） number of peripheral blood, the percentage of lymphocytes, and IgG concentration in the experimental group were significantly higher than those in the control group on Day 14, 28 and 42 （ P 〈 0.01 ）. [ Conclusion] The Chinese herbal additive can enhance the lactation performance and immunologic function of dairy cows.

Value Addition to Red Sediment Placer Sillimanite Using Microwave Energy and in Depth Structural and Morphological Characterization of Mullite

This paper deals with the effect of microwave energy for mullite formation from placer sillimanite. A mullite formation is seen when 60 % SiC and 5% binder are used with the composite charge material, i.e. sillimanite (60%) and Al2O3 (40%). The maximum temperature of the microwave sintering furnace achieved is 1355°C at 2450 W microwave power. Addition of 10 % binder to the same charge material with 60% SiC, the furnace temperature achieved is 1384°C at microwave power 1900 W. Mullite is formed within 25 minutes from the sillimanite, under the above experimental conditions. Whereas under the similar additive conditions, the mullite formed from sillimanite in conventional furnace heating, it took 3 hours at 1300°C. XRD data show the mullite phase for both the products obtained from microwave sintering furnace and conventional furnace. FESEM image analysis shows the mullite formations, SiC fibrous cluster and alumina needles in microwave treated sample. Thus microwave heat source is much more effective for value addition to red sediment placer sillimanite to form mullite in compare to conventional furnace.

Application of Technology of Additive Manufacturing in Radiators and Heat Exchangers

Radiators and heat exchangers play a key role in the long-term and stable operation of the equipment. The emergence of additive manufacturing technology has released the freedom of design, enabling many innovative structures of radiators and heat exchangers to be manufactured. The paper reviews the application of additive manufacturing in new radiators and heat exchangers. The technology of additive manufacturing boosts the development of new radiators and heat exchangers, which improves heat dissipation performance and heat exchange efficiency. This paper will provide a new idea and method for the development of radiators and heat exchangers via the application of additive manufacturing.

Comprehensive Evaluation and Prediction of Enhancement of Boiling Heat Transfer with Additives

A model of evaluation and prediction of enhancement of boiling heat transfer with additives has been propoeed according to fuzzy fundamentals. Correlative appraisement of boiling heat transfer augmentation was done with the model based on 39 additives which were tested by the authors and other researchers. The results show that the evaluation of 35 additives is consistent with experiments, which means that the accuracy of the model is 89.7 percent. In addition, the prediction of the ability of boiling heat transfer enhancement with sodium oleate,polyethylene glycol and Tween-40 is also in good agreement with correspondent experiments.

Effects of Chinese Herb Additive on Milk Yield and Anti-heat Stress Ability of Holstein Cows

[Objective] To explore the effects of Chinese herb additive on milk yield and anti-heat stress ability of Holstein diary cow. [Method] A total of 36 Holstein cows at same parity and with similar milk yield were randomly divided into three groups, namely, control group, Chinese medi- cine group I and Chinese medicine group I1. The cows in the Chinese medicine group I were fed basal diet containing 4% compound Chinese herb additive; those in the Chinese medicine group II were fed basal diet containing 3% compound Chinese herb additive; and those in the control group were fed common basal diet. All cows in the three groups were analyzed comparatively. [Result] Supplementing some compound Chinese herb ad- ditive into basal diet increased milk yield and anti-heat stress ability of Holstein cows, besides, it also decreased cow diseases like cow mastitis. The Chinese medicine group I generated the highest economic benefit of practical production. [ Conclusion] Supplementing Chinese herb additive in- to basal diet is an effective way to relieve heat stress and increase milk yield.

增材制造技术在散热器件研制中的应用与最新进展

5G技术的普及以及高性能算力系统的快速发展,导致电子器件的功率不断增加,因此对散热器件的性能提出更高要求。优化散热器件的结构是提高散热性能的重要途径之一。然而,传统制造工艺在处理复杂结构时存在一定的局限性,限制了对更高性能散热器件的探索。增材制造技术采用逐层累加的方式,可制备出具有复杂内部几何形状的结构,从而制造出更高性能的散热器件。本文对增材制造技术在散热器件领域的研究进展进行了综述。首先,介绍了增材制造技术的常用方法和基础材料;其次,综述了利用增材制造技术研发微流道散热器、热管/均热板、热沉以及其他散热器的最新进展;最后,归纳了散热结构的优化设计方法。本文着眼于利用增材制造技术制备具有优化结构的散热器件,为应对电子器件、航空航天、 5G通讯、移动设备、汽车、相控雷达、柔性穿戴等领域日益增长的散热需求提供了有益的参考。

中药添加剂对热应激生长兔生长性能、屠宰性能、肠道微生态和血清生化指标的影响

本试验旨在研究饲粮中添加中药添加剂对热应激生长兔生长性能、屠宰性能、肠道微生态和血清生化指标的影响。选取48只健康、体重相近的2月龄新西兰白兔,随机分成2组,每组24只(公母各占1/2),单笼饲养。在夏季热应激状态下,对照组饲喂基础饲粮,中药组在基础饲粮中添加1%中药添加剂。预试期7 d,正试期42 d。结果表明:1)对照组和中药组之间末重、平均日增重和料重比差异不显著(P>0.05)。中药组的成活率较对照组有所增加(83.3%vs.70.8%,P>0.05)。2)中药组的半净膛重和半净膛率显著高于对照组(P<0.05)。3)中药组的盲肠内容物干物质含量显著高于对照组(P<0.05),盲肠内容物乙酸和丙酸含量有低于对照组的趋势(P=0.092)。4)对照组和中药组之间盲肠内容物细菌总数和alpha多样性差异不显著(P>0.05)。中药组的盲肠内容物栖粪杆菌属、普氏栖粪杆菌相对丰度显著高于对照组(P<0.05),盲肠内容物阿克曼菌属和大肠杆菌相对丰度有高于对照组的趋势(P=0.080、P=0.088)。5)中药组的粪便球虫圆小囊数有低于对照组的趋势(P=0.082)。6)对照组和中药组之间血清生化指标差异不显著(P>0.05)。综上所述,饲粮中添加中药添加剂可调控热应激生长兔肠道微生态,提高屠宰性能和肠道健康。

激光增材制造与连接GH4169合金的热处理工艺研究

采用激光增材制造技术制备了GH4169合金母材样品,并采用相同的工艺参数实现了母材的激光增材连接,检测了不同热处理状态下合金的拉伸性能,分析了性能改变的内在机理。结果表明:凭借激光增材制造技术热影响区小的优势,热处理前后母材与连接区域处微观组织的演变基本一致。沉积态合金呈典型的柱状晶组织,且二次枝晶并不发达,γ+Laves共晶相呈条带状和岛链状沿晶界分布;均匀化+固溶处理后Laves相发生分解并回溶入基体,并伴随着柱晶的粗化;当进行双重时效处理时Laves相的分布状态发生改变。不同热处理工艺试样的拉伸性能均高于同合金铸态指标,热处理对Laves相的含量和分布状态的改变是影响其强度和塑性的主要因素。