Papers by Keyword: Powder Forging

Abstract: Process maps according to Parasad et al. are already widely used to make statements about the formability of materials and their forming energy. However, these process maps only apply to conventional incompressible materials. At the TU Bergakademie Freiberg, these process maps have already been extended for particle-reinforced incompressible solid materials with a homogeneous particle distribution. The next step is to adapt the model for compressible particle-reinforced matertials so that they can also be used in powder metallurgy. The problem here is that the volume decreases as a result of compaction during powder forming. In powder metallurgy, however, compaction plays an important role. On the one hand, the compaction of the components leads to an increase in the material properties. On the other hand, pores pose a high risk of fractures and cracking. For this reason, it is the aim of this paper to make the existing process maps for incompressible materials usable for compressible materials by corresponding adaptations of the models prevailing in powder metallurgy. Furthermore, the effects of a homogeneous particle distribution and a graded particle distribution within the TRIP matrix composites on the process maps will be investigated. For this reason, process maps are produced in the temperature ranges between 700 – 1050 °C, with forming speeds of 0.001 – 100 s^-1 and residual porosity of 10 – 30 %. For this purpose, specimens with corresponding residual porosity and homogeneously distributed ZrO₂ 5 vol.%, 10 vol.%, 15 vol.% and 20 vol.% as well as a graded layer structure of corresponding ZrO₂ proportions are prepared. With the aid of these specimens, flow curves are determined and adjusted at appropriate temperatures and forming speeds during compression tests. The energy dissipation and an instability map are then modelled from these flow curves and a process map is derived. It was found that with increasing ZrO₂ content in the homogeneous and the graded structure, the areas that allow damage-free forming become smaller. The same applies with decreasing residual porosity. Nevertheless, the areas, which allow failure-free forming, are larger than the possible forming areas of solid components. However, the power dissipation efficiency of incompressible specimens is significantly lower than that of compressible specimen [1]. In addition, it was observed that with increasing ZrO₂ content and decreasing residual porosity, the efficiency of the power dissipation in the formable areas decreases. It was also found that the distribution of the reinforcing particles has a significant influence on the flow curves and the associated process maps, then the graded specimen do not represent a superposition of the individual process maps of the homogeneous specimens.

Abstract: Blended elemental powder metallurgy is a cost effective approach to produce near net shape titanium alloy parts; however, the residual pores remaining in sintered parts are detrimental to the mechanical properties. In this study, elemental powders (Ti, Al and Fe) were used to produce the Ti-5Al-2Fe alloy by a powder forging process, involving cold compaction, vacuum sintering, forging and heat treatment. The residual pores of the sintered parts were removed completely by forging at the temperature of 1250oC. The effect of solution and aging and mill annealing heat treatments on the mechanical properties of the forged Ti-5Al-2Fe parts were studied. It is found that the ductility of the forged Ti-5Al-2Fe parts is improved significantly by both solution and aging treatment and mill annealing, without decreasing their ultimate tensile strength, which sits around 1000 MPa. The enhancement of the mechanical behaviour is justified via understanding the evolution of the residual porosity and of the microstructural features of the materials.

Abstract: The hot deformation and densification behaviors of sintered P/F-10C50 steel were investigated by hot compression tests on Gleeble-1500 thermal mechanical simulator at the temperature ranging from 900 °C to 1000 °C and the strain rate ranging from 0.1 s^-1 to 10 s^-1. The flow and densification characteristics of the tested specimens at different deformation temperatures and strain rates were studied. The flow stress of the sintered steel persistently increases until the end of the test as the result of matrix and geometric work hardening. The higher deformation temperature and strain rate are conductive to the healing of the pores and promote the densification of the sintered steel, while the higher deformation temperature and lower strain rate impede the densification. The constitutive equation of the sintered steel is established by the means of stepwise regression. The flow stresses predicted by the established constitutive equation are in good agreement with the experimental values, and the correlation coefficient (R) and the average absolute relative error (AARE) are 0.9931 and 3.52%, respectively. These results demonstrate the hot deformation behaviors of the sintered P/F-10C50 steel are excellently predicted by the established constitutive equation.

Abstract: Ti6Al4V is one of the best known and studied titanium alloy for the optimization of the thermo-mechanical treatments. The Ti-forgings represent a valid opportunity for the aircraft manufacturers and designers because of high tensile and fatigue properties. Nevertheless the total-cost reduction of the manufacturing-chain requires both: the ability to manufacture nearer-shaped components by mean of forging-process-modification and less final machining (material scraps). Even if Ti6Al4V is a well known alloy, any process parameters modification introduced still represents a challenge for the metallurgists and manufacturers.The idea, at the base of the present work, has been the feasibility study of forging experiments in the Beta-field using Hot Isostatic Pressed (HIP) powders billets. The preliminary compression tests has been carried out in laboratory and the results have been validated in a industrial Forging-Workshop. The deformation behavior of Ti6Al4V HIPped powders during high temperature deformation tests is reported. Laboratory compression and tensile tests have been coupled with relaxation tests in order to achieve robust data about strain rate sensitivity m-coefficient and activation energy Q.The obtained results have been fitted for the assessment of generalized exponential deformation law. The final result is a “Dorn model” that takes into account and compares all the results from the three different deformation tests: compression, tensile and relaxation. The deformation tests have been carried out at temperatures ranging from 1173 K up to 1373 K and strain rate from 0,01 s^-1 up to about 1 s^-1, trying to describe the high temperature complex shape forging operations.Finally the recorded deformation curves has been used for modeling by means of FEM DeformTM code the deformation process and microstructure evolution by means of an Avrami type law.

Abstract: Sintered P/M ferrous compacts containing up to 0.8% phosphorous have attractive set of mechanical and magnetic properties. Large phosphorous additions increase the shrinkage during sintering to such a degree that the tolerances of the sintered component may become adversely affected. Further, the sintering process requires more time and energy and is hence costly. To overcome the above problems, powder forging route has been used. In this process encapsulated Fe- P based alloy powder is heated and forged it into slabs. These were hot rolled to produce sheet and wires. Phosphorous addition improves the final density of the resulting product. It also improves the soft magnetic properties. All the alloys exhibited excellent workability.

Abstract: Powder forging combines powder metallurgy and forging technology, thus possess the advantages of both processes that result in both stronger and yet more versatile products with complicated geometry and arbitrary alloy compositions. For complete filling up, predicting the power requirement and final face width is an important feature of the powder forging process. In this paper, a finite element method is used to investigate the forging force, the final face width and the density variation of the spur gear powder forging process. In order to verify the FEM simulation results, the experimental data are compared with the results of the current simulation for the forging force and the final face width of spur gear. The influences of the parameters such as modules, number of teeth, the initial relative density, the ratio of the height to diameter of billet and friction factor on the forging force and the final face width of the billets are also examined.

Abstract: In recent years powder metallurgy method P/M because of complicated parts production ability is used widely, but existence of porosities in this products will decrease mechanical properties in this method, but advanced powder metallurgy methods like powder forging P/F with having profits of powder metallurgy P/M because of visible reduce in porosities will decrease powder metallurgy problems. One of the mechanical properties that is effected by the porosity is wear properties ,in this research by comparison between two groups of specimen, that first group made by powder metallurgy method that had 14% amount of porosities and second group that made by powder forge method P/F that had less than 1% amount of properties and change in wear parameters in both of groups we survey wear properties and we compare wear rate and mechanism result is showing visible relation between wear properties and amount and morphology of porosities.

Abstract: Three types of composite materials, Al-10Ni-6Ce (at%)/pure Al (Vf=0.3), Al-10Ni- 6Ce/Al-3.6Mn (Vf=0.3) and Al-10Ni-6Ce/Al-5.5Mg (Vf=0.3), and monolithic Al-10Ni-6Ce alloy were successfully fabricated to a fully dense rod-shaped bulk form having a diameter of about 10mm by adopting a powder forging or extrusion process using amorphous Al-Ni-Ce powder together with crystalline pure Al, Al-Mn and Al-Mg powders. The monolithic Al-Ni-Ce specimen forged at 648K showed a very high compressive strength of 1.3GPa without exhibiting any compressive plastic strain. All of the composite specimens forged at 648K gained a compressive plastic strain with the considerable sacrifice of strength. In contrast, Al-Ni-Ce/Al-Mg composite specimen extruded at 648K showed a noticeably high compressive strength of 1.2GPa with the compressive plastic strain of 0.5%. The extruded Al-Ni-Ce/Al-Mn composite specimen also exhibited a considerably high compressive strength (1.1GPa) accompanied with plastic strain (0.2%).

Abstract: Powder forging is used for heavy-loaded parts (rings of rolling-contact bearings, gears etc.) production. Rolling contact fatigue is material property values of which characterize possibility of practical utilization of such parts. Rolling contact fatigue of some steels obtained out of prealloyed powders Astaloy CrM, Atomet 4601, Atomet 4901 and powder blends iron-carbon-nickel by hot forging is studied in the present paper. Effect of various kinds of heat and thermomechanical treatment on rolling contact fatigue is determined. Thermomechanical treatment provides optimal values of rolling contact fatigue. In this case steel structure contains up to 40% of retained metastable austenite which is transformed to martensite on trials. Thus typically crack is generated on residual pores and non-metallic inclusions instead of martensite zones in wrought steels.

Abstract: Two atomized alloy powders, those chemical compositions are Al-10Si-5Fe-1Zr and Al- 10Si-5Fe-4Cu-2Mg-1Zr, were pre-compacted by cold pressing with 350MPa and subsequently hot forged at temperatures ranging from 653K to 845K and at an initial strain rate of 10-2/s in order to produce bulk cylindrical type alloys with the diameter of 10 mm. The addition of Cu and Mg into the present alloy causes a decrease in the eutectic reaction temperature of Al-10Si-5Fe-1Zr alloy from 841K to 786K and results in a decrease of flow stress at the given forging temperature. TEM observation revealed that in addition to Al-Fe based intermetallics, Al2Cu and Al2CuMg intermetallics appeared to display the alloying effect additionally. The volume fraction of intermetallic dispersiods increased by the addition of Cu and Mg. Compressive strength of the present alloys was closely related to the volume fraction of intermetallic dispersoids.