Preparation of Ni60-WC Coating by Plasma Spraying, Plasma Re-melting and Plasma Spray Welding on Surface of Hot Forging Die

In order to produce the hear-resistant inner layer of hot-forging die, the plasma spraying and plasma re-melting and plasma spray welding were adopted. Substrate material was W6Mo5Cr4V2, including 10%, 20%, 30% tungsten carbide （WC） ceramic powder used as coating material to obtain different Nickel-based WC alloys coating. Micro-structure and micro-hardness analysis of the coating layer are conducted, as well as thermophysical properties for the coating layer were measured. The experimental results show that the coating prepared with 70%Ni60, 30%WC powder has the best properties with plasma spray welding, in which the micro-hardness can achieve 900HV, meanwhile it can improve the thermal property of hot-forging die dramatically.

STUDY ON DESIGN TECHNIQUES OF A LONG LIFE HOT FORGING DIE WITH MULTI-MATERIALS

A new design technique for the long life hot forging die has been proposed. By finite element analysis, the reason .for the failure of hot forging die was analyzed and it was concluded that thermal stress is the main reason for the failure of hot forging die. Based on this conclusion, the whole hot forging die was divided into the substrate part and the heat-resistant part according to the thermal stress distribution. Moreover, the heat-resistant part was further subdivided into more zones and the material of each zone was reasonably selected to ensure that the hot forging die can work in an elastic state. When compared with the existing techniques, this design can greatly increase the service life because the use of multi-materials can alleviate the thermal stress in hot forging die.

Ni60-SiC Coating Prepared by Plasma Spraying, Plasma Re-melting and Plasma Spray Welding on Surface of Hot Forging Die

In order to produce the hear-resistant inner layer of hot-forging die, plasma spraying and plasma re-melting and plasma spray welding were adopted. Substrate material was W6Mo5Cr4V2, including 10%, 20%, 30% SiC ceramic powder used as coating material to obtain different Ni-based SiC alloys coating. Micro-structure and micro-hardness analysis of the coating layer were followed, as well as thermophysical properties for the coating layer were measured. The experimental results show that the coating prepared with 70% Ni60, 30% SiC powder has best properties with plasma spray welding, in which the micro-hardness can achieve 1100 HV, meanwhile can improve the thermal property of hot-forging die dramatically.

Carbide Coating Preparation of Hot Forging Die by Plasma Processing

To meet the performance requirements of hot forging die heat resistant layer, the Ni60-SiC coating, Ni60-Cr3C2 coating, and Ni60-WC coating were prepared using W6Mo5Cr4V2 as substrate material with 30%SiC, 10%Cr3C2, 30%WC powder by means of plasma spraying and plasma spray re-melting and plasma spray welding, respectively. Microstructure of each carbide coating was analyzed, micro-hardness was tested, and mainly thermal parameters of coating were detected. The experimental results show that using plasma spray welding, the performance of 70%Ni60/30%SiC powder is the best, and its micro-hardness can achieved 1100HV, showing good thermal-physical property.

Hot forging of Mg-4Al-2Ba-2Ca(ABa X422) alloy and validation of processing map

A cup-shaped component of Mg-4 Al-2 Ba-2 Ca（ABa X422） alloy was forged in the temperature range of 300-500 °C and at speeds in the range of 0.01-10 mm/s with a view to validate the processing map and study the microstructural development. The process was simulated through finite-element method to estimate the local and average strain rate ranges in the forging envelope. The processing map exhibited two domains in the following ranges：（1） 300-390 °C and 0.0003-0.001 s^-1, and（2） 400-500 °C and 0.0003-0.3 s^-1 and both represented dynamic recrystallization（DRX）. The map revealed a wide flow instability regime at higher strain rates and temperatures lower than 400 °C, in which flow localization occurred. Forgings produced under conditions of the above two domains were sound and symmetrical, and had finer grain sizes when being forged in the first domain. However, when being forged in the flow instability regimes, the alloy fractured before the final shape was reached. The experimental load-stroke curves for the conditions within the domains correlated well with the simulated ones, whereas the curves obtained in the instability regime were uneven.

Optimizing Hot Forging Process Parameters of Hollow Parts Using Tubular and Cylindrical Workpiece： Numerical Analysis and Experimental Validation

CAE （computer aided engineering） evaluates the forging process virtually to optimize the industrial production. The numerical and experimental investigations of forging process of a hollow part are important in industrial point of view. This study has been focused on the development of a 3D elastic-plastic FEM （finite element model） of hot forging to evaluate the forming process of hollow parts. The validity of this method was verified through a laboratory experiment using aluminum alloy （AA6351） with medium geometric complexity. The distributions of effective strain, temperature, metal flow and strength were analyzed for two different initial workpieces （tubular and cylindrical）. It was observed that both initial workpieces can be used to produce the final hollow part using the numerical simulation model. The results showed that the numerical analyses predict, filling cavity, calculated strength, work temperature and material flow were in agreement with the experimental results. However, some problems such as air trapping in the die causing incomplete filling could not be predicted and this problem was resolved experimentally by drilling small holes for air release in the dies.

Numerical simulation and physical analysis for dynamic behaviors of P/M TiAl alloy in hot-packed forging process

The hot forging of large-scale P/M TiAl alloy billet deformation was investigated based on a joint application of Deform-3D-based numerical simulation and physical simulation techniques.The temperature dependence on the thermal and mechanical properties of the billet was considered and the optimum hot working temperature of packed TiAl alloy was 1150-1200 °C.Based on the simulation,the material flow and thermo mechanical field variables,such as stress,strain,and temperature distribution were obtained and the relationships of load—displacement and load—time were figured out.To verify the validity of the simulation results,the experiments were also carried out in a forging plant,and a pancake with diameter of 150 mm was obtained exhibiting a regular shape.

A Physically Based Dynamic Recrystallization Model Considering Orientation Effects for a Nitrogen Alloyed Ultralow Carbon Stainless Steel during Hot Forging

The nitrogen alloyed ultralow carbon stainless steel is a good candidate material for primary loop pipes of AP1000 nuclear power plant. These pipes arc manufactured by hot forging, during which dynamic recrystallization acts as the most important microstructural evolution mechanism. A physically based model was proposed to describe and predict the microstructural evolution in the hot forging process of those pipes. In this model, the coupled effects of dislocation density change, dynamic recovery, dynamic recrystallization and grain orientation function were con sidered. Besides, physically based simulation experiments were conducted on a Gleeble 3500 thermo-mcchanical sire ulator, and the specimens after deformation were observed by optical metallography （OM） and clectron back scat toted diffraction （EBSD） method. The results confirm that dynamic recrystallization is easy to occur with increasing deformation temperature or strain rate. The grains become much finer after full dynamic recrystallization. The model shows a good agreement with experimental results obtained by OM and EBSD in terms of stress strain curves, grain size, and recrystallization kinetics. Besides, this model obtains an acceptable accuracy and a wide applying scope for engineering calculation.

Hot-forging Die Cavity Surface Layer Temperature Gradient Distribution and Determinant

Based on the car front-wheel-hub forging forming process of numerical simulation, the temperature gradient expression of forging model cavity near the surface layer was got ten, which illustrates that the forging temperature gradient is related to forging die materials thermal conductivity, specific heat and impact speed, and the correlation coefficient is 0.97. Under the different thermal conductivity, heat capacity and forging speed, the temperature gradient was compared with each other. The paper obtained the relevant laws, which illustrates the temperature gradient relates to these three parameters in a sequence of thermal conductivity 〉 impact speed〉 specific heat capacity. To reduce thermal stress in the near-surface layer of hot forging cavity, the material with greater thermal conductivity coefficient and specific heat capacity should be used.

Dual phase titanium alloy hot forging process design： experiments and numerical modeling

Titanium alloys materials when both good weight reduction are required are considered desirable mechanical properties and at the same time. This class of materials is widely used in those fields （aeronautics, aerospace） in which common steels and light-weight materials, e.g., aluminum alloys, are not able to satisfy all operative service conditions. During the last decade, forg- ing of titanium alloys has attracted greater attention from both industrial and scientific/academic researchers because of their potential in providing a near net shaped part with minimal need for machining. In this paper, a numerical model of the forging sequences for a Ti-6A1-4V titanium alloy aerospace component is presented. The model was tested and validated against experimental forgings. The model is then applied to predict loads final microstructure and defects of an aeronautical component. In addition to metal flow and die stresses, microstructural transformations （α and β phases） are considered for the determination of proper process parameters. It is found that transformation from α/β to β phase during forging and reverse transformations in post-forge cooling needs to be considered in the computational model for reasonable prediction of forging loads and product properties.

PHYSICAL SIMULATION OF INTERFACIAL CONDITIONS IN HOT FORMING OF STEELS

In the last few years,substantial experimental simulation and mumerical modelling hare been carried out in IMMPETUS to characterise the interfacial heat transfer and friction conditions during hot forging and rolling of steels. Emphasis has been placed on the influence of the oxide scale which forms on the steel workpiece. In the present paper, the experimental methods used for investigating interfacial heat transfer and friction conditions are described. Theses include hot flat rolling of steel slabs and hot axi- symmetric forging of steel cylinders and rings.Temperature measurements and computations demon- strate that for similar conditions, similar conditions, the effective interfacial heat transfer coefficients (IHTC) derived for hot rolling are significantly higher than those for forging, mainly due to the contribution of scale cracking during rolling. On the basis of experimental observations and numerical analysis,physical models for interfacial heat transfer in forging and rolling have been established. In addition, hot' sandwich' rolling and hot tensile tests with finite element modelling have been carried out to evaluate the hot ductility of the oxide scale.The results indicate that the defomation, cracking and decohesion behaviour of the oxide scale depend on deformation temperature, strain and relative strengths of the scale layer and scale - steel interface.Finaly, friction results from hot ring compression tests and from hot rolling with forward/backward slip measurements are reported.

FINITE ELEMENT SIMULATION AND OPTIMIZATION OF MULTISTAGE WARM/HOT FORMING FOR OUTER RACE

A multistage warm/hot forming is simulated for the cross grove outer race ofconstant velocity joint, using a thermo-mechanical coupled rigid viscoplastic finite element method,and specially some problem for process development and die design are analyzed. A forming testshows that computed results have good agreement with experimental results. Above obtained resultscan be applied to development of multistage warm/hot forming process and die design for outer race.

Microstructure and Deformation Behavior of Ti-10V-2Fe-3Al Alloy during Hot Forming Process

The microstructure evolution and formability of Ti-10V-2Fe-3Al alloy related to the initial microstructures and processing variables were investigated during hot forming process. The experimental results show that the α-phase growth is controlled by solute diffusion during the heat treatment processes. Four different microstructures were established by combinations of several heat treatments, and Ti-10V-2Fe-3Al alloy shows excellent formability both above and below the β transus temperature. The alloy possesses low deformation resistance and active restoration mechanism during the deformation. A constitutive equation describing the hot deformation behavior of Ti-10V-2Fe-3Al alloy was obtained. Higher fl ow stress was observed for the acicular morphology of α phase in microstructures with large aspect ratios as compared with that of small aspect ratios. Due to the dynamic recovery in soft β phase, and the dynamic recrystallization and breakage of acicular α-phase, fl ow softening occurred signifi cantly during deformation. Dynamic recrystallization also occurred especially in the severely deformed regions of forged parts.

Effects of forging parameters on uniformity in deformation and microstructure of AZ31B straight spur gear

The effects of forging parameters on the deformation and microstructure distributions of as-forged straight spur gears wereinvestigated by finite element(FE)simulation and statistical analysis method.Spur gear forging using the movable cavity die designwas investigated by integrating the FE method with the microstructure evolution models for AZ31B magnesium alloys.The requiredinputs such as flow stress curves and microstructure evolution models,were obtained through the Gleeble thermal mechanical testingand quantitative metallography analysis method.Numerical simulation and experimental examination confirm that both thedeformation and microstructure are non-uniformly distributed in the as-forged gears.Decreasing deformation temperature orincreasing strain rate is beneficial to obtaining fine-grained microstructure but is harmful to the uniformity in deformation ormicrostructure.The level of the non-uniformity results from the complex shape of gear and the friction between the billet and dies,which is closely associated with the characteristics of flow stress curve.

Analysis of Forging Dies Coated with Tungsten Carbide through HVOF Processing

In this paper we present a performance evaluation of thermal spraying coated hot forging dies conducted in a production line. The High Velocity Oxy-Fuel process was used for the deposition of a tungsten carbide coating, which is characterized by its optimal adherence and low porosity. A metallurgical characterization of the layer was previously done, in order to obtain reference information to assist in the interpretation of the practical tests results. The coated die allowed an increase in productivity of 37.5%, besides better dimensional stability results through the process and legibility of printed numbers.

Microstructural evolution during hot and cold deformation of Ti-36Nb-2Ta-3Zr-0.35O alloy

The Ti-36Nb-2Ta-3Zr-0.350 （mass fraction, %） （TNTZO） alloy was produced by cold isostatic pressing and sintering from elemental powders, followed by hot and cold deformation. The effects of deformation process on microstructures and mechanical properties were investigated using the SEM, TEM, OM and the universal material testing machine. Results show that the alloy can be easily hot forged and cold swaged due to the fine-grained microstructure. Only after cold swaging by 85%, the alloy shows the typical ＂marble-like＂ structure. And thecold deformation is accompanied by stress-induced a＂ phase transformations. Moreover, both the strength and the ductility of the alloy are significantly improved by hot and cold working.

Material driven workability simulation by FEM including 3D processing maps for magnesium alloy

The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.

Microstructure and Thermal Physical Parameters of Ni60-Cr_3C_2 Composite Coating by Laser Cladding

To satisfy performance and long life requirements for hot forging die,Ni60-Cr3C2 composite coatings were prepared on the high-speed steel W6Mo5Cr4V2 using laser cladding technology.Laser clad coatings with different ratios of Ni60：Cr3C2 were investigated by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,energy-dispersive X-ray analysis（EDX） and micro-hardness tester,respectively.Specific heat capacity and thermal conductivity were measured by Laser Thermal Constant Meter.Thermal expansion coefficient and elastic modulus were measured by Dynamic Mechanical Thermal Analyzer and Electro-Hydraulic Servocontrolled Testing System,respectively.The results indicated that Ni60＋50wt% Cr3C2 composite coating had dense and homogeneous structure,as well as a metallurgical bonding with the substrate.With the increase of Cr3C2 content,volume of chromium-containing compounds in the composite coating increased,microhardness increased and microstructure refined.The thermal physical parameters results showed that Ni60＋50wt% Cr3C2 composite coating was overall worse than W6Mo5Cr4V2,but had a higher hot yield strength to alleviate hot fatigue and surface hot wear of hot forging die during hot forging and thus improve the service life of hot forging die.

PHSICAL MODELLING AND PROCESSING OF Ti-6Al-4V ELI

Titanium has been widely used as the implant materials of joint prostheses. This paper simulates the microstructures of the hot forged titanium knee joint component by physical modeling. Ti-6Al-4V ELI were deformed by GLEEBLE 2000 hot deforma- tion simulator in compression mode to determine the hot workability, in the range of 900 to 1100℃, with the strain rates between 0.05 to 5 s^(-1). Test results derived from specimens processed by on-cooling test and on-heating test were compared, thereby estimating the effect due to thermal history. The forging process of Ti-6Al-4V ELI tibial base plate of knee joint prostheses was design based on the workability data obtained.

Microstructural evolution of TiAl base alloy during three-stepped thermo-mechanical treatment

A TiAl base alloy ingot with a height to diameter ratio of 2.2 was broken down by multiple step canned forging. The microstructures after every deformation and subsequent recrystallization were observed by optical microscopy. Results show that at the first step the reduction should be carefully controlled in case of double bulge and crack of the ingot. After the first annealing, recrystallization occurred at the deformed grain boundaries and inside the grain. The recrystallized microstructure is favorable for further deformation. After the second deformation and annealing, coarsening of the lamellae occurred and the microstructure became equiaxed. By the final deformation and subsequent recrystallization, the coarse lamellar colony can be refined to about 20 μm, and homogeneous microstructure was obtained from the ingot with a large initial height to diameter ratio.