HEAT TRANSFER BEHAVIOR OF SUPERALLOY DROPLETS DURING SPRAY FORMING

Based on the Newtonian heat transfer formulation and classical heterogeneous nucleation theory, a mathematical model has been established to predict the profile of flight velocity, heat transfer coefficient, temperature, solid fraction and cooling rate of atomizing droplets for a superalloy. The results indicated that above parameters change with different droplet size and flight distance. The changing trend as well as the mechanism for the change are described and discussed.

SF-6D在慢性阻塞性肺疾病病人健康效用值测量中的应用研究进展

对六维健康调查简表的构成、测量学特性、在慢性阻塞性肺疾病(COPD)病人健康效用值研究中的应用情况进行综述,并提出存在的问题与展望,以期为进一步开展相关研究提供参考。

Microstructure evolution and phase transformation of traditional cast and spray-formed hypereutectic aluminium-silicon alloys induced by heat treatment

Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and spray forming （SF） processes, were investigated by differential scanning calorimetry （DSC） and scanning electron microscopy （SEM） combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that A17Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K and 800-815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.

Production of high strength Al-Zn-Mg-Cu alloys by spray forming process

High strength Al Zn Mg Cu alloys were produced by spray forming process, and compacted by hot extrusion. The results show that the as deposited billets have fine grained microstructure and low porosity. After heat treatment, mechanical properties increase greatly: tensile strength up to 754 MPa, yield strength up to 722 MPa, fracture elongation up to 8%, and elastic modulus up to 72 GPa, respectively. [

Simulation of jet-flow solid fraction during spray forming

A numerical model was developed to simulate the jet-flow solid fraction of W18Cr4 V high-speed steel during spray forming. The whole model comprises two submodels: one is an individual droplet model, which describes the motion and thermal behaviors of individual droplets on the basis of Newton's laws of motion and the convection heat transfer mechanism; the other is a droplet distribution model, which is used to calculate the droplet size distribution. After being verified, the model was used to analyze the effects of parameters, including the initial gas velocity, deposition distance, superheat degree, and the ratio of gas-to-metal mass flow rates, on the jet-flow solid fraction. Finally, an equation to predict the jet-flow solid fraction directly and conveniently according to the parameters was presented. The values predicted by the equation show good agreement with those calculated by the numerical model.

Shape-predicted model of spray forming rod under scanning atomization

A model for simulating the spray forming process with scanning atomizer was developed.Models for the scanning atomization and the deposition processes were coupled together in order to obtain a new description of the spray forming process.The model,which is able to predict the shape of a spray-formed billet prepared with scanning atomizer,was established after analyzing the changes in droplet size and density distribution along the r-axis in the spray cone in scanning atomization.The effects of the two kinds of atomization were compared,showing that the scanning atomization is good for deposition.

Modeling and Simulation of the Microstructure Evolution of the Gas-atomized Alloy Droplets during Spray Forming

In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on the population dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains. The model is coupled with droplets heat transfer controlling equations and solved for AI-4.5 wt pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.

Experimental and mathematical modeling of metal spray forming process

The metal spray forming process was examined using mathematical simulation and verified through the prototyping evaluation at Baosteel＇ s test and development facilities. The mathematical model comprised of four sections, including jet gas flow in the deposition chamber;single droplet behavior along its trajectory path;probability and statistical analysis of droplet mass behavior, and forecast of the shape and temperature distribution of the billet during the spray forming process.

Microstructure and forming characteristics of spray-formed M42 high speed steel

M42 high speed steel （HSS）, a high grade alloy, was produced using the spray forming technology. Optical metallography （OM）,X-ray diffraction （XRD） and scanning electron microscope （SEM） were used to investigate the microstructures of the as-sprayed M42 HSS and the as-atomized powders. It is found that as-sprayed M42 HSS is composed of martensite, retained austenite and carbides. The grain size, as well as the morphology, size and distribution of the carbides have been greatly improved compared with those of the as-cast M42 steel （ a traditional process）. The size of the powder obtained at a high cold speed was ranged from 50 μm to 100μm in diameter. Its representative microstructures include dendrite, dendritic fragments, a mixture of dendrites, equiaxed grains and dendritic fragments,and equiaxed grains. The rapid solidification in the spray forming is a key factor to cause the refinement of the M42 HSS.

The Heat Treatment Behavior of Super-High Strength Aluminum Alloys by Spray Forming

In order to understand the stress corrosion behavior of super-high strength aluminum alloys by spray forming, different aluminum alloys by different heat treatment was made. The results showed that the alloy with peak aging has the most sensitive stress corrosion cracking, the crack can even be seen using eyes;the alloys with two step aging were better than one step aging alloys, the alloys has not been found stress corrosion cracking.

Application of a Novel Multilayer Spray Forming Technology in the Preparation of Large Dimension Aluminium Alloy Blanks

Principle of multilayer spray forming and preparation technique of tubes and billets by it were presented and described in the article. The marked characteristic of multilayer spray forming technology is the to and fro movement of spray system, so the preform is deposited layer by layer with the surface of the deposit retaining relatively low temperature during the spray forming process. The two outstanding advantages of multilayer spray forming are as follows: suitable for manufacturing large dimension blanks, higher solidification cooling rate. Now Al Fe V Si alloy (8009) and SiC particle reinforced aluminium alloy metal matrix composite billets of 300 600 mm in diameter and tubular blanks of size up to 650 mm in outer diameter, 360 mm in inner diameter and 1 200 mm in length have been made with the technology. After extrusion, the material has good properties.

Plasma Spray Forming

In the course of plasma spray, the plasma jet is comprehensively functioned by such effects as thermal pinch, magnetic pinch and mechanical compression and the flow is jetting at a high speed, the energy is concentrated and its center temperature is so high as to reach upwards of 15 000 ℃ which is capable of melting various kinds of materials inclusive of ceramic, it has a broad applied prospects in the fields of automobile, electronics, telecommunications, medical treatment, air navigation & space navigation and light industries etc because of being able to rapid fabricate thin-walled metals, ceramics and alloy parts thereof, metal moulds, functionally gradient material moulds and so on, and it has become a research spotlight for the scholars. The technology of plasma spray forming (PSF) is introduced, and the two different kinds of technique presented in this paper are studied. Some typical links in the course of technical process is also analyzed, including original prototype fabrication and surface treatment, post-treatment of formed workpiece and demoulding methods. When spraying, it should select the appropriate making methods of prototype according to the dimensions, shapes and forming accuracy as required by the formed parts. At the same time, it should be paid to the characteristic of the material for the prototype. The main purpose of surface treatment of the prototype is to raise the quality of formed parts and ensure the integrity demoulding of the coating. The method of the prototype’s surface treatment is closely related to the demoulding method, which is mainly comprised of destructive demoulding, non-destructive demoulding and composite demoulding, and is key technology in PSF. In order to eliminate these intrinsic defects and improve its performance, the fabricated parts can be given the necessary post-treatment so as to further raise the mechanical strength and surface quality. There are many methods for the post-treatment such as chemical reinforcment, metal melt-infiltration, laser-melting and self-propagating high-temperature synthesis, etc., all these methods can decrease the porosity and raise the quality of coating and service performance; whereas the finishing machining can improve the surface roughness of spray formed parts. In the course of spray forming, affected by such complex and complicated factors as electric field, the entangled ambient gas and introduced powder, as a result, it shall induce the instability of the spray condition and affect the forming quality. This paper has, on the basis of large quantity of experiments, analyzed every links in the course of PSF, summarized and evaluated the main factors affecting on the quality of formed parts, such as prototype characteristic, characteristic of plasma jet, powder characteristic, spray gun and spray parameters. The experiments prove that the process of PSF is simple and the cost is lower in rapid tooling with complex and complicated fine patterns, and PSF is apt to form special-shape and thin-walled parts made of some protective materials so as to protect those fragile workpieces. Therefore PSF is a new technology with broad and brilliant prospects of development.

Spray forming and mechanical properties of a new type powder metallurgy superalloy

The deposited billet of a new type powder metallurgy （PM） superalloy FGH4095M for use in turbine disk manufac- turing has been fabricated using spray forming technology. The metallurgical quality of the deposited billet was analyzed in terms of density, texture, and grain size. Comparative research was done on the microstructure and mechanical properties between the flat disk preform prepared with hot isostatic pressing （HIP） and the same alloy forgings prepared with HIP followed by isothermal forging （IF）. The results show that the density of the spray-formed and nitrogen-atomized deposit billet is above 99% of the theoretical density, indicating a compact structure. The grains are uniform and fine. The billet has weak texture with a random distribution in the spray deposition direction and perpendicular to the direction of deposition. A part of atomizing nitrogen exists in the preform in the form of carbonitride. Nitrogen-induced microporosity causes the density reduction of the preform. Compared with the process of HIP＋IF, the superalloy FGH4095M after HIP has better mechanical properties at both room temperature and high temperature. The sizes of the 7~ phase are finer in microstructure of the preform after HIP in comparison with the forgings after HIP＋IE This work shows that SF＋HIP is a viable processing route for FGH4095M as a turbine-disk material.

Numerical simulation of tube profile growth during spray forming process

Spray forming is a new type of metal material forming process,which can produce metal blanks such as billet, tube,plate etc. A mathematical model has been developed to forecast the shape evolution of tube billets during the spray forming process. The atomizer mass flux as ,radial distribution coefficient bs, draw velocity and diameter of mandrel were considered in this model and the influence of different parameters such as metal flowrate, draw velocity of mandrel, diameter of mandrel on the tube＇ s shape change were simulated and analyzed in this paper. The simulation results obtained from this model can be provided to engineers as reference.

A study on mathematical simulation of spray forming process

An integrated approach for modeling the entire spray forming process is presented in this paper, and the program for the simulation is developed. The whole spray forming process can be divided into four calculation processes and the basis for the analysis is the classical k -ε turbulence model which was used to simulate the flow field of gas formed in the chamber. In the atomization model the flow field of gas is coupled with formation, velocity and location of droplet. By means of the above mathematical model, the process of spray forming was simulated.

High Speed Steel and WC Particle-Reinforced Composites Produce by Spray Forming

The process of spray forming utilized to fabricate WC particle-reinforced high speed steel composites has been studied. In addition, microstructures and mechanical properties of M2 high speed steel and its composites made by spray forming have been analyzed. The results show that the primary carbides of high speed steel are of two types: MC and MbC. With the increase in flight distance, the morphology of the primary carbides varies from fine fish-bone-like to islandlike and both bending strength and hardness increase. With the increase in volume fraction of WC reinforcement particles,hardness of the composites increases considerably, but bending strength, however, appears to be a decreasing tendency.

The numerical simulation of the movements and thermal states of atomized metal droplets in the spray forming process

Numerical simulation was performed in an atomizing chamber to investigate the movements and thermal states of the atomized metal droplets in the spray forming process. The velocity, temperature and solid fractions of metal droplets with different diameters and under different atomizing pressures were investigated. The results indicate that a higher atomizing pressure results in the increased flying velocity of the metal droplets and a decrease in the cone-shaped angle formed by their flight paths. Synchronously, the cooling of the metal droplets is accelerated and the time of the complete solidification process is shortened. Under the same atomization pressure, large metal droplets have a lower flying speed and a lower rate of temperature decrease in the atomizing chamber than small metal droplets. In addition, metal droplets flying along the edge of the atomizing region cool faster than those flying in the core region.

SF-36在神经症病人中应用的信度及效度研究

目的 评价健康状况调查问卷(The Short-Form-36 Health Survey,SF-36)在神经症病人中的信度和效度。方法 由专业医生对53例心身科门诊及住院患者评定焦虑自评量表(self-rating anxiety scale,SAS)、抑郁自评量表(self-rating depression scale,SDS)和SF-36,4周后予以重测。对量表的内部一致性、重测信度及效标关联效度等指标进行分析。结果 SF-36的Cronbach's α系数为0.7581,各维度的Cronbach's α系数较好,重测后各项目的相关系数均在0.284～0.796之间。SF-36各维度分与SAS、SDS总分间。除躯体功能,躯体健康功能导致的角色受限,情感功能所致的角色受限外,均与SAS总分呈明显负相关,除躯体功能、躯体健康功能导致的角色受限,躯体疼痛,情感功能所致的角色受限外,SDS总分呈明显负相关。结论 SF-36具有较好的信度和效度,部分分量表能较好反映神经症病人的情绪状态,基本适用于神经症病人生活质量评价。

NRS2002和MNA-SF评价老年入院患者营养状况的比较研究

目的:利用营养风险筛查2002(NRS2002)和简易营养评价精法(MNA-SF)评价老年入院患者的营养状况,了解NRS2002和MNA-SF与传统营养评价方法的相关性。方法:选择北京医院消化内科、呼吸内科、神经内科、心内科、肾内科新入院老年患者162例,进行人体测量和生化指标检测,包括体重指数(BMI)、血红蛋白(HB)、总蛋白(TP)、白蛋白(ALB)、肌酐(CR)、尿素氮(BUN)、甘油三酯(TG)、总胆固醇(TC)等。计算两种方法与传统指标的相关性。结果:根据Spearman相关分析,NRS2002与BMI、CC、AMC、ALB、HB呈显著的负相关关系(P<0.05),MNA-SF与BMI、CC、AMC、ALB、HB呈显著的正相关关系(P<0.05)。NRS2002及MNA-SF与TP、CR、BUN、TG、TC无显著相关关系。结论:NRS2002和MNA-SF可以作为内科老年入院患者的营养评估方法。