Net Shape Components Research Articles

Elastic moduli of sintered powders with application to components fabricated using selective laser melting

We show that overlapping sphere packs provide useful models for the microstructure and elastic properties of sintered bronze powders. In the early stages of sintering the dilated sphere (or cherry-pit) model is superior, while at low porosities the sintered powders are more accurately described by freely overlapping spheres. The dilated sphere model accurately predicts Young’s modulus for materials produced by the selective laser melting of metal powders. This will help improve the match between designed and actual properties of net-shape components made using this process.

Fabrication of CuSiC Composite by Powder Metallurgy Route

Copper-based composite now is a potential material for various applications, while powder metallurgy processing technique is an alternative for high temperature processing materials and net shape component. In this research, Cu-based composite containing 10-50 vol% SiC fibers was fabricated by employing the powder metallurgy route. The mixtures of SiC fibers and Cu particles were blended in a ball milling machine with the addition of ethanol at 150rpm. Then, the mixtures were uniaxially compacted into a ɸ13.5mm cylindrical pallet and followed by sintering in vacuum furnace from 800-950°C for 4 hours. The density of the composite decrease with increasing SiCf and density as high as 87% for 10vol% SiCf/Cu matrix sintered at 800°C had been achieved. The Vickers hardness of 774MPa also had been achieved for 10vol% SiCf/Cu matrix but sintered at 900°C.

Young’s modulus and damping in dependence on temperature of Ti–6Al–4V components fabricated by shaped metal deposition

Young’s modulus and damping behavior is investigated by the impulse excitation technique in vacuum up to 1100 °C for Ti–6Al–4V components, fabricated by shaped metal deposition (SMD). This is a novel additive manufacturing technique where near net-shape components are built layer by layer by tungsten inert gas welding. The Young’s modulus decreases linearly from 118 GPa at room temperature to 72 GPa at 900 °C, followed by a stronger decrease up to 1000 °C and during the first heating a plateau thereafter. The damping exhibits an exponential increase with temperature superimposed by two peaks around 700 and 900 °C during the first heating. During cooling and follow-up cycles only the damping peak around 700 °C appears. The change in Young’s modulus and the damping behavior is interpreted by different processes like α/β transformation, O alloying and grain boundary sliding. These results indicate that components fabricated by SMD contain a non-equilibrium α phase which transforms to the β phase at higher temperatures than the equilibrium α phase. Furthermore, the vacuum between 2.4 and 5.3 × 10−4 mbar proved at high temperatures to be not good enough to rule out the contamination by O, which leads to α casing, stiffening, and hardening.

Microstructural evolution and mechanical properties of back-extruded Al 7075 alloy in the semi-solid state

The thixoforming process is a new method for manufacturing complicated and net shape components through which high strength materials can be formed more easily. In this study 7075 Al alloy which has low extrudability has been thixoformed by backward extrusion process. The recrystallisation and partial melting (RAP) route was used to obtain the semi-solid feedstocks for thixoforming. Microstructural evolution during partial remelting was studied at temperatures for times. Results showed that a fine and globular microstructure can be obtained by the RAP route. The results showed that high semisolid isothermal temperature would increase the liquid volume fraction and accelerate the spherical processing of the solid particles. Furthermore at long holding time, the globular grains coarsened slightly and the average grains size are increased. The experimental results showed that when the semisolid billet is hold at 580°C with the holding time, less than 30 min, the microstructure of the billet is composed of spherical grains and remnant liquids, the average grain size are smaller than 100 μm. So the remelted billet is suitable for thixoforming. In this paper, a back-extruding of 7075 Al alloy with a high solid fraction in the semi-solid state at 580°C for 10 min was performed. Mechanical properties of thixoformed components at room temperature were examined. Tempering treatment T6 has been applied after thixoforming to investigate the effects of heat treatment on mechanical properties of thixoformed parts. The tensile properties and low hardness values in the as-thixoformed 7075 Al alloy were improved by subsequent heat treatment. Post-forming heat treatment is one of the key parameters for improving the mechanical properties of thixoformed parts.

Isothermal and Near Isothermal Processing of Titanium Alloys

Isothermal and near isothermal forging are specialized metal processing techniques which are used for producing critical aeroengine components out of advanced materials such as titanium alloys. The process can be used to produce net / near net shape components leading to optimum utilization of materials. As titanium alloys are highly sensitive to temperature and strain rate, these processes help to deform them under slow and controlled strain rates. Further, these processes can be combined with other conventional and non conventional metal forming processes to refine the microstructure. For example, multiaxial isothermal forging coupled with pack rolling can be used to produce thin sheets out of titanium alloys with submicron grain size. The refined structure exhibits superplastic characteristics at low temperatures and high strain rates. This lower temperature superplastic characteristic can be exploited to establish technologies for producing various components. The paper throws light on the capabilities of isothermal forging process and its variants. Defence Science Journal, 2011, 61(1), pp.72-80 , DOI:http://dx.doi.org/10.14429/dsj.61.321

Thermal expansion and lattice parameters of shaped metal deposited Ti–6Al–4V

Thermal expansion and lattice parameters are investigated up to 1100 °C for Ti–6Al–4V components, fabricated by shaped metal deposition. This is a novel additive layer manufacturing technique where near net-shape components are built by tungsten inert gas welding. The as-fabricated SMD Ti–6Al–4V components exhibit a constant coefficient of thermal expansion of 1.17 × 10 −5 K −1 during heating up to 1100 °C, not reflecting the α to β phase transformation. During cooling a stalling of the contraction is observed starting at the β transus temperature. These high temperature experiments denude the α phase of V and enrich the β phase. The development of the lattice parameters in dependence on temperature are observed with high temperature X-ray diffraction. The unit cell volumes derived from these parameters are at room temperature larger for the α than for the β phase. With increasing temperature the unit cell volume of the β phase increases stronger than the one of the α phase resulting in a similar unit cell volume at the β transus temperature. These observations are interpreted as an indication for as-fabricated the SMD components being in a non-equilibrium state and reaching equilibrium during the slow heating and cooling during of the two different high temperature experiments.

Influence of the Particle Size on Phase Transformation Temperatures of Ni-49at.%Ti Shape Memory Alloy Powders

It is important to control the martensitic transformation start temperature (Ms) of Ti–Ni alloys because it determines the temperature range over which the shape memory effect and superelasticity appear. Powder metallurgy (PM) is known to provide the possibility of material-saving and automated fabrication of at least semi-finished products as well as net-shape components for NiTi alloys. In this study powder with different particle sizes was subjected by gas atomization. The evolution of the control the martensitic transformation start temperature (Ms) was studied by differential scanning calorimetry. The effect of the particle size of powders on the transformation temperatures behaviors was discussed.

Spin Formability of Al-6061 Aluminum Alloy Pre-Forms Obtained via Liquid Forging

There are growing demands from the precision engineering industries for components that are net or near net shape while striving to reduce material wastage during the manufacturing process. This study investigates the spin formability of liquid forged Al-6061 pre-forms into near net shape cylindrical components with high aspect ratios. The liquid forging process offers very significant materials savings by providing pre-forms for the spin forming process. The end products are near net shape components with very good mechanical properties. Results from this study indicate that liquid forging is able to supply Al-6061 pre-forms, otherwise machined from solid bars, which are sufficiently formable for spin forming. The microstructure of a spin formed liquid forged pre-form is also indiscernible from that of a fully machined pre-form from extruded bar stock. As such, spin forming of liquid forged pre-forms has the potential to reduce material wastage and hence production costs.

Improvement in silicon morphology and mechanical properties of Al–17Si alloy by melt conditioning shear technology

A hypereutectic Al–Si alloy containing 17 wt-%Si was synthesised using melt conditioning by advanced shear technology. The conventional methods often generate primary Si phase with starlike and platelet morphologies exhibiting lower ductility and wear resistance for the alloy. A new rheoprocessing method, the melt conditioning high pressure die casting (MC-HPDC) process, has been developed for manufacturing near net shape components. The MC-HPDC process adapts the well established high shear dispersive mixing action of a twin screw mechanism. Quantitative analysis revealed considerable spheroidisation and a uniform distribution of primary Si particles. Compared with those produced by conventional HPDC, MC-HPDC samples have improved tensile strength, ductility and wear resistance.

Characterization of interfacial microstructures in 3003 aluminum alloy blocks fabricated by ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state processing technique that uses ultrasonic vibrations to bond metal tapes into near net-shaped components. The benefits of UAM include the production of complex geometries and the incorporation of smart materials to produce functional composites and join dissimilar metals. The majority of the current research focuses on processing parameter optimization to eliminate macroscopic void formation at the interface. The present study utilizes ion-channeling contrast imaging from a focused ion beam, electron backscattered diffraction and transmission electron microscopy to examine microstructural changes induced during the UAM process. The results indicate that there is a bonding mechanism due to localized plastic deformation of asperities that undergo recrystallization and grain growth across the interface. Evidence for localized solidification microstructures, generated due to frictional sliding between the sonotrode horn and the tape material, is also presented.

Consolidation Process in Near Net Shape Manufacturing of Armstrong CP-Ti/Ti-6Al-4V Powders

This paper summarizes our recent efforts to develop the manufacturing technologies of consolidated net-shape components by using new low-cost commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy powders made by the Armstrong process. Fabrication processes of net shape/ near net shape components, such as uniaxial die-pressing, cold isostatic pressing (CIP), sintering, roll compaction and stamping, have been evaluated. The press-and-sinter processing of the powders were systematically investigated in terms of theoretical density and microstructure as a function of time, pressure, and temperature. Up to 96.4% theoretical density has been achieved with the press-and-sinter technology. Tensile properties of the consolidated samples exhibit good ductility as well as equivalent yield/ultimate tensile strengths to those of fully consolidate materials, even with the presence of a certain amount of porosity. A consolidation model is also under development to interpret the powder deformation during processing. Net shape components made of the Armstrong powder can successfully be fabricated with clearer surface details by using press-and-sinter processing.

Investigation of mechanical properties of 7075 Al alloy formed by forward thixoextrusion process

The thixoextrusion process is a new method for manufacturing complicated and net shape components through which high strength materials can be formed more easily. In this study 7075 Al alloy which has low extrudability has been thixoformed by forward extrusion process. As it is known conventional extrusion of 7075 Al alloy has been very difficult due to high strength and multi-phase microstructural characterization. In this research, by applying the advantages of semisolid processing, the applied pressure for extrusion is decreased and desired mechanical properties were reached near the standard predictable properties for wrought 7075 Al alloy under T6 tempering conditions, for example tensile and yield strength and hardness of samples of thixoextrusion product sufficiently agree with same expected properties of wrought 7075 Al alloy and only elongation is decreased along this process.

Analysis on Microstructure of AlSi7Cu5 Alloy by Slope Near-Liquidus Method

SSM(Semi-solid metal) forming has been developed to become a novel technology in the 21st century for the formation of near net shape components, competing with conventional casting and forging technologies. In this paper, the casting microstructure and its change during remelting of AlSi7Cu5 alloy casting by slope near-liquidus method were researched. Experiments show that it has a significant impact on microstructure by cooling method, the thermal conductivity of the casting mold and casting method. The microstructure of AlSi7Cu5 alloy obtained by slope near-liquidus method at 600°C is uniform and small equiaxed Its average grain diameter is about 55.2um, and its average grain size roundness is about 2.13. The reheated microstructure which can be applied in thixo-forming preferable will be obtained by keeping constant temperature 25min at 580°C.

Solidification of high Nb containing TiAl based alloys

Casting of titanium aluminides is an attractive processing route for production of near net shape components: turbocharger wheels, valves and aero-engine components are presently at the heart of casting developments. Among the casting alloys under consideration are a number of niobium rich TiAl based alloys that contain low boron additions for grain refinement and minor additions of other elements to enhance creep resistance. An essential condition that must be met to achieve grain refinement is a solidification pathway competed via β-(Ti), e.g. a pathway that avoids peritectic growth of α-Ti. In this contribution we describe the microsegregation analysis of a unidirectionally solidified sample from the ternary alloy Ti–45Al–8Nb. The corresponding solidification path is discussed on the basis of thermodynamic calculations and is shown to closely follow Scheil predictions with some amount of back-diffusion for aluminium. The analysis indicates that the nucleation undercooling for peritectic α (Ti) in the deep mushy zone is significant.

New manufacturing process for thermally sprayed prepregs with local UD fiber reinforcement for semi solid forming of light metal MMC

Thermal spraying and thixoforging technologies can be combined in a new manufacturing method for the production of light metal matrix composites. This paper describes the production of unidirectional (UD) and tailored local fiber reinforced MMC based on this new method. For manufacturing of UD fiber reinforced metals, fiber prepregs are produced by coating of fiber bundles with light metal matrix material. For further processing to the final MMC, these prepregs are laminated, heated up and densified by thixoforging to near net-shape components. Compared to conventional technologies for the integration of fibers in light metal matrices, like squeeze casting, hot pressing and diffusion bonding, this method offers the possibility to realize complex component geometries with short cycle times. However, the focus of this paper lies on the flexible processing of fiber prepregs with local, already near net-shape fiber reinforcement by continuous fiber deposition and simultaneous coating with the matrix alloy by thermal spraying. As a case study, the manufacturing of a wheel rim with local reinforcement in the central area will be discussed.

Aero-Engine Titanium from Alloys to Composites

The aero-engine has provided the major drive for the development of new improved titanium alloys in recent years. This paper covers these developments from the workhorse alloy Titanium 6/4 and it’s higher temperature stable mates through to the more exotic intermetallic materials and on to their reinforcement with ceramics. The use of Ti6/4 alloy is now widespread throughout the aero space industry providing a good combination of strength at moderate temperatures (~300°C) a relatively low density and a wide range of processing options ranging from castings to forgings to powder HIP and diffusion bonding. Alloy development for the aero-engine essentially concentrated on either increasing the temperature capability and creep resistance or increasing the strength at intermediate temperatures. Alloys such as Ti 6242 and IMI 834 were aimed at compressor disc applications with operation up to around 600°C. Improvements resulted from compositional control and thermal processing to optimize the microstructure for creep and fatigue. High strength intermediate temperature capability (~500°C) alloys were also developed (Ti6246) where higher levels of molybdenum balance the alpha strengthening additions. The drive for lighter weight led to the development of titanium intermetallic systems. Alloys such as 45-2-2XD and Alloy 7 have been the subject of much research and manufacturing development over the last 20 years, demonstrating that they are capable of operating at temperatures well above those of conventional titanium. More recently, alloys with higher additions of Nb and Ta have shown improved mechanical properties and offer promise to extend the application of TiAl above 700°C. In parallel with intermetallic developments combining titanium alloys with the extreme high strength of ceramic fibres has proved irresistible and many ways to produce titanium composites have been developed. The majority of application development has focused on Ti6/4 alloy as the matrix although other matrix alloys have been investigated and tested in U.S. engine demonstrators. Recently a combination of Ti-22Al-26Nb disks reinforced with orthorhombic MMC ran for over 100 hours in an engine test. However, none of these niche composite systems has yet made the transition into large volume production and the fibre reinforced Ti6/4 system probably offers the greatest potential for implementation. The main barrier to the take up of both advanced intermetallics and titanium composites is the cost of raw materials and processing. The challenge still exists to produce net shape components and provide weight savings at an acceptable cost. This will be the key to future exploitation.

Research on the Hot Precision Processing of TiAl Alloys

γ-TiAl components due to their unique properties are on the verge of industrial application for increasing operation temperature and improving energy efficiency, especially in aerospace and automobile areas. This paper describes the recent developments of hot precision processing in ingot metallurgy technology including investment casting, canned forging and sheet rolling of TiAl alloys. Alloys development and the melting technology were discussed. Investment casting of TiAl alloys has been successfully developed to manufacture net-shape components. Research aimed at producing TiAl sheets through canned forging and rolling is introduced.

Laser aided direct metal deposition of Inconel 625 superalloy: Microstructural evolution and thermal stability

Direct metal deposition technology is an emerging laser aided manufacturing technology based on a new additive manufacturing principle, which combines laser cladding with rapid prototyping into a solid freeform fabrication process that can be used to manufacture near net shape components from their CAD files. In the present study, direct metal deposition technology was successfully used to fabricate a series of samples of the Ni-based superalloy Inconel 625. A high power CO 2 laser was used to create a molten pool on the Inconel 625 substrate into which an Inconel 625 powder stream was delivered to create a 3D object. The structure and properties of the deposits were investigated using optical and scanning electron microscopy, X-ray diffraction and microhardness test. The microstructure has been found to be columnar dendritic in nature, which grew epitaxially from the substrate. The thermal stability of the dendritic morphology was investigated in the temperature range 800–1200 °C. These studies demonstrate that Inconel 625 is an attractive material for laser deposition as all samples produced in this study are free from relevant defects such as cracks, bonding error and porosity.

Mechanical properties of Ti-6Al-4V specimens produced by shaped metal deposition

Shaped metal deposition is a novel technique to build near net-shape components layer by layer by tungsten inert gas welding. Especially for complex shapes and small quantities, this technique can significantly lower the production cost of components by reducing the buy-to-fly ratio and lead time for production, diminishing final machining and preventing scrap. Tensile testing of Ti-6Al-4V components fabricated by shaped metal deposition shows that the mechanical properties are competitive to material fabricated by conventional techniques. The ultimate tensile strength is between 936 and 1014 MPa, depending on the orientation and location. Tensile testing vertical to the deposition layers reveals ductility between 14 and 21%, whereas testing parallel to the layers gives a ductility between 6 and 11%. Ultimate tensile strength and ductility are inversely related. Heat treatment within the α+β phase field does not change the mechanical properties, but heat treatment within the β phase field increases the ultimate tensile strength and decreases the ductility. The differences in ultimate tensile strength and ductility can be related to the α lath size and orientation of the elongated, prior β grains. The micro-hardness and Young’s modulus are similar to conventional Ti-6Al-4V with low oxygen content.

Fundamentals of semisolid magnesium molding

Fundamentals of magnesium injection molding, including the feedstock characteristics, mechanisms of slurry generation, and various processing routes, are outlined in this article. Detailed features of molded structures are correlated with processing techniques and properties of net-shape components.