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.

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.

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.

Microstructure and Mechanical Properties of Spray Deposited Ni-based Superalloys

Three kinds of superalloys were prepared by spray deposited process. The analysis results of microstructures and mechanical properties indicate that the spray deposited preforms with higher integral densification and the oxygen content in each kind of superalloy was very low. The microstructures are consisted of fine grain without dendritic equi-axed. The spray deposited superalloys possessed good ductility. The forging experiment displays that even though the once deformation of spray deposited GH742 alloy more than 60%, the crack can not be found. Meanwhile, the mechanical properties of spray deposited superalloys are significantly increased.

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.

SPRAY FORMED NICKEL-BASE SUPERALLOYS

In this paper,part of the research and development work in the field of spray formed superalloys at BIAM of China is briefly summarized. With an experimental spray forming facility,whose melting capacity is suitable for making disk and columnar shaped integral-dense and clean Ni-base superalloy preforms with low oxygen content,fine grain, uniform chemistry and improved forgeability, a series of Ni-base superalloys have been spray atomized and deposited, among which three alloys have been chosen for microstructural and mechanical properties evaluation.

INVESTIGATION INTO HOT DEFORMATION BEHAVIOR OF SPRAY FORMED SUPERALLOY GH742

In order to evaluate the deformation characteristics of spray formed superalloy GH742and determine the appropriate forging procedure of the alloy on this basis, the influenceof deformation temperature and strain rate on the ductility of spray formed GH742was investigated by using the Gleeble-3500 thermal-mechanical testing machine. It isshown that the forgeability of spray formed GH742 is better than conventional GH742by ingot metallurgy because of refined grain structure and enhanced chemical homo-geneity of spray formed GH742. In the temperature range of 1020 to 1100℃, theductility of spray formed GH742 is dependent on the deformation temperature and isincreased linearly in proportion to the increment of deformation temperature, whichis more than 40% at 1020℃ and more than 60% at the temperature between 1100and 1140℃. Furthermore, the results indicate the flow stress is affected considerablyby the deformation temperature and strain rate. In the temperature range of 1020 to1140℃, the maximum flow stress of spray formed GH742 increases with the incrementof strain rate and decreases with the increment of the deformation temperature.

Innovative technologies for powder metallurgy-based disk superalloys: Progress and proposal

Powder metallurgy（PM） superalloys are an important class of high temperature structural materials, key to the rotating components of aero engines. In the purview of the present challenges associated with PM superalloys, two novel approaches namely, powder preparation and the innovative spray-forming technique（for making turbine disk） are proposed and studied.Subsequently, advanced technologies like electrode-induction-melting gas atomization（EIGA）, and spark-plasma discharge spheroidization（SPDS） are introduced, for ceramic-free superalloy powders. Presently, new processing routes are sought after for preparing finer and cleaner raw powders for disk superalloys. The progress of research in spray-formed PM superalloys is first summarized in detail. The spray-formed superalloy disks specifically exhibit excellent mechanical properties. This paper reviews the recent progress in innovative technologies for PM superalloys, with an emphasis on new ideas and approaches, central to the innovation driving techniques like powder processing and spray forming.

Microstructure,Tensile Properties and Heat Treatment Process of Spray Formed FGH95 Superalloy

The potential of spray forming for microstructural refining can be attractive to the production of superalloys.A200mm spray formed FGH95superalloy round billet that was produced using a single atomizer has considerably homogeneous,small,equiaxed grains.The measured oxygen content is 2×10-5,and the measured porosity is only 0.6%.The achieved yield of deposit is in a good range of about 73.6%.The microstructure and tensile properties of nickel-based spray formed FGH95superalloy are analyzed.Also,effects of heat treatment on microstructure were discussed.The results show that the spray formed FGH95superalloy has higher isotropy in tensile property due to itsγ′phase homogeneous distribution and less defects in the microstructure.Regarding processing procedures,the different heat treatment processes affect the microstructure andγ′phase homogeneous distribution of spray formed FGH95superalloy.

Microstructural Characterization of Spray Formed FGH4095 Superalloy During Hot Deformation

In order to study the hot workability and to optimize the processing parameters for spray formed FGH4095 superalloy, thermal compression tests for spray formed FGH4095 superalloy have been finished by using a Gleeble 1500 thermal simulated test machine at the strain rates of 0.01-10.0 s 1 and temperatures of 1 050-1 140 ℃. The effects of strain rate and deformation temperature on the true stress-true strain curves and microstructure evolution were investigated. The results show that the generation of dynamic recrystallization （DRX） depends sensitively on deformation temperature. When the temperature was lower than 1080 ~C, long and＂ narrow necklace grains were shown in the microstructure. When the temperature increased to 1 140 ℃, new recrystallization grains were genera-ted. The size and shape of X＇ precipitates in the grains have a very important effect as factors of hindering sufficient migration of dislocations on plastic deformation. The result of thermal processing map is in accord with the micro-structure observation, and the best material thermal processing temperature is above 1 128 ℃.

Analysis of Solidification in Spray Atomized and Codeposited Metal-matrix Composites Part Ⅱ:Reinforcement Injection and Deposition

The influence of the injection of reinforcing particles (for the production of metal matrix composites and of the droplets-to-substrate heat transfer on the resulting microstructural uniformity of spray atomized and codeposited composite material is analyzed. The reinforcement particles injection velocity has to be limited between an upper and a lower critical values. in order to ensure entrapment into the matrix droplets in flight. The thermal history of the injected droplets during the deposition stage is calculated with the assumption that the in-flight solidifying droplets reach the substrate while containing still at least 20% liquid volume fraction, in order to avoid porosity of the deposited material. The substrate to pouring-tube orifice distance where that condition is achieved depends strongly on the atomization pressure and the convective heat transfer coefficient of the substrate. It is demonstrated that 'tailoring' the microstructures and the reinforcement volume percent in the deposited material is feasible. The critical process parameters : the atomization pressure, the melt flow rate. the substrate to pouring-tube orifice distance, the reinforcement particles injection location and rate can all be adequately chosen in order to obtain any desired microstructure, grain size, reinforcement volume percent, with the additional benefit, if wanted, of rapid solidification processing

Effect of P/M value on the preforms and microstructures of spray formed 70Si30Al alloy

A novel 70Si30Al alloy was prepared by the spray forming process for electronic packaging materials. The effect of the ratio of atomization pressure to metal melt mass flux rate （P/M） on the preforms and microstructures of the spray-deposited 70Si30Al alloy was studied. The results indicate that the PIM value has a considerable influence on the formation of the preforms and the optimal value is in the range of 0.209-0.231 MPa/（kg.min^-1）. The microstructure of the spray formed 70Si30AI alloy is fine and homogenous. The primary silicon phases distributing in the aluminum matrix evenly are fine and irregular. The aluminum matrix is divided into two groups： supersaturated α-Al phase or α-Al phase and Al-Si pseudoeutectic phase or Al-Si eutectic phase.

Microstructural Features of Spray-Deposited Immiscible Bearing Alloys Al-43Sn and Al-7Sn-1.3Cu-1.3Ni

Two commercial grade aluminum based immiscible bearing alloys were spray-deposited using convergent-divergent type of nozzle. The processing parameters for spray-deposition were adjusted in such a way that most of the droplets arrived on the deposition substrate in either liquid or semi-liquid state. The microstructural features of spray-formed and as-cast alloys are compared. In spray-formed alloys equiaxed grains were observed. The cell boundaries and intercellular regions were observed to be decorated with sub-micron sized particles whereas in normal casting the second phase was observed to be segregated along grain boundaries. The morphology and distribution of second phase were observed to have similarity with those in over-spread and atomized powders produced under similar processing conditions. The microstructural features observed with variation in spray conditions are discussed in detail.

Design and Atomization Characteristic of Laval-style Annular Slot Nozzle

Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.

Microstructure of a Spray Deposited Intermetallic Compound Alloy of Ni-Al-Mo System

The microstructure of a spray deposited intermetallic compound alloy of Ni-Al-Mo system（Ni3Al-Mo intermetallic compound alloy） prepared by a spray atomization deposition was studied in detail by using optical metallography,XRD,DTA,SEM,TEM,HREM and computer simulation.The preform consists of uniform and equiaxial grains,ranging from 10-40 μm,with some microporosity.Besides the main phases of the matrix alloy γ＇ and γ,Ni2Mo and Ni3Mo phases are also found within the γ network.A new Ni enriched phase in the γ phase was identified to have face-centered cubic structure with a lattice constant α=1.09 nm and space group Fm3m.

A NEW PARTICLES ADDING TECHNIQUE FOR PREPARATION OF METAL MATRIX COMPOSITE USING SPRAY DEPOSITE

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ON THE INSTABILITY IN GAS ATOMIZATION

The instability theory of fluid flow is applied in gas atomization and the results show that the instability of interfacial wave is the main cause of gas atomization. The size of the droplets and its change with parameters are also studied, the results are compatible with the experiments.

WC Particle High Speed Steel Composites Manufactured by Ultrasonic Spray Forming

The process of manufacturing high speed steel matrix composites reinforced by WC particles was studied. The changes in microstructures and mechanical properties of composites with WC particles were also investigated. The results show that increasing the deposition height can significantly enhance the bending strength and hardness of the alloy, and that the fishbone like carbide ledeburite structure gradually diminishes as the WC particles content increases. It was discovered that the hardness of the composites increases due to the increase of pointlike carbide ledeburite, accompanying the breaking of the fishbone like and the net like carbides. However, the bending strength deteriorates due to excessive WC particles increasing the brittle interfacial phase.