Qianchu Liu

Evaluation of microstructure and fatigue properties in laser cladding repair of ultrahigh strength AerMet® 100 steel

The metallurgy and fatigue properties were evaluated for the laser cladding of AerMet® 100 powder on AerMet® 100 substrate. Working with small scale tensile and fatigue samples causes an overextended HAZ due to the constant heating applied on a small thermal mass. The limited heat input causes major processing issues with inter-run porosity observed. The microstructure observed in both the clad and Heat-affected Zone (HAZ) is (1) inhomogeneous and nonuniform and (2) hard and brittle martensitic structure. As a result, the yield strength is reduced by 37%, ultimate tensile strength (UTS) reduced by 13%, elongation reduced by 57%, and the fatigue life is reduced significantly.

Microstructural features and cracking of laser cladding on 7XXX aluminium alloys with AL-12%SI powder

Increasing interest is to apply advanced laser technology for surface cladding on aluminium alloys or corresponding components, in order to repair the damaged surfaces caused by fatigue or corrosion and to restore the original properties. However, the mechanical or corrosion properties strongly depend on the microstructures. This paper presents the study of the microstructural features in both the clad layer and the Heat-affected zones (HAZs). The aluminium-12%silicon (Al-12%Si) was used for cladding on 7xxx series aluminium alloys.The main features in the clad layer are fine α-aluminium columnar dendritic grains plus some interdendritic aluminium-silicon eutectic. There exit silicon particles between the dendrite arms. Silicon particles in eutectic are smaller and less angular. But the microstructure at the centre is considerably finer. Coarse grains occurred in the HAZs. Cu segregation occurred at both the grain boundaries and the grain interior, resulting in a Cudepleted α-phase next to a Cu-rich eutectic, forming dark strips-liquation film at the grain boundaries. The energy dispersive x-ray (EDX) spectrum indicated that the liquation film is copper-rich with other elements such as Fe, Zn and Mg elements (Al2CuMg & Al7Cu2Fe particles). These liquation films are often associated with cracking and corrosion because of the brittleness.Increasing interest is to apply advanced laser technology for surface cladding on aluminium alloys or corresponding components, in order to repair the damaged surfaces caused by fatigue or corrosion and to restore the original properties. However, the mechanical or corrosion properties strongly depend on the microstructures. This paper presents the study of the microstructural features in both the clad layer and the Heat-affected zones (HAZs). The aluminium-12%silicon (Al-12%Si) was used for cladding on 7xxx series aluminium alloys.The main features in the clad layer are fine α-aluminium columnar dendritic grains plus some interdendritic aluminium-silicon eutectic. There exit silicon particles between the dendrite arms. Silicon particles in eutectic are smaller and less angular. But the microstructure at the centre is considerably finer. Coarse grains occurred in the HAZs. Cu segregation occurred at both the grain boundaries and the grain interior, resulting in a Cudepleted α-phase next to a Cu-rich eutec...

Repair of aircraft components by laser cladding process

With aging fleets in-service parts damage from corrosion, wear or debris impact is becoming more prominent. Replacement of these damaged parts can be expensive and slow and therefore have a significant impact on fleet availability and sustainment costs. Laser powder technology is regarded as an advanced manufacturing technology, which could change the way fleet operators think about long term sustainment. Parts could quickly be manufactured or repaired in country from CAD files.With the advances in laser technology, laser cladding is one of laser technologies, which is becoming an industrial repair technology. The technology is at a point where it can potentially be used to repair or refurbish the non-critically structural aircraft components. Its adaptability to a variety of materials and applicability to solve and/or minimise a variety of induced damage is strength. The current major issue is the certification of laser clad repairs or manufactured parts. At present certification tends to be on a case by case basis.This paper reports on the successful use of laser cladding to repair non-critical structural aircraft components. This paper summaries the current research and applications and of the research on laser cladding of steel alloys, which has being carried out by Defence Science and Technology Organisation and Defence Materials Technology Centre, Melbourne, Australia. An overview of the certification process for a typical non-critical structural component repair is also provided.With aging fleets in-service parts damage from corrosion, wear or debris impact is becoming more prominent. Replacement of these damaged parts can be expensive and slow and therefore have a significant impact on fleet availability and sustainment costs. Laser powder technology is regarded as an advanced manufacturing technology, which could change the way fleet operators think about long term sustainment. Parts could quickly be manufactured or repaired in country from CAD files.With the advances in laser technology, laser cladding is one of laser technologies, which is becoming an industrial repair technology. The technology is at a point where it can potentially be used to repair or refurbish the non-critically structural aircraft components. Its adaptability to a variety of materials and applicability to solve and/or minimise a variety of induced damage is strength. The current major issue is the certification of laser clad repairs or manufactured parts. At present certification tends to be on a case by...

Mechanical properties of selective laser melted Ti-6Al-4V with different layer thickness

Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal Deposition (DMD) or Additive Manufacturing (AM) processes. Due to the nature of its layer-by-layer process, the microstructures from the bottom layers to the top layers are significantly different due to highly thermal gradient induced by laser beam combined with different cooling rates at each built layer. The SLM process parameters such as laser power, scan speed, layer thickness, hatch spacing etc have a major influence on the mechanical properties of the material fabricated. The relationship between mechanical properties associated with microstructure and process parameters is critical for the manufacture of functional components. The understanding of this relationship will help to facilitate future studies on manufacture and repair of titanium alloy parts/components with SLM technology. Increase in layer thickness will lead to increase in productivity. However, such an increase may impact on the mechanical properties of the material.This paper presents the effect of powder layer thickness on the mechanical properties (tensile and fatigue) of manufactured specimens. The experimental results in this investigation showed that the increase in layer thickness from 30 to 90 µm did not affect the tensile strengths but the ductility was dramatically reduced. The fatigue life was also significantly decreased. The results indicate that the SLM process needs to be optimised for a thicker powder layer case.Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal Deposition (DMD) or Additive Manufacturing (AM) processes. Due to the nature of its layer-by-layer process, the microstructures from the bottom layers to the top layers are significantly different due to highly thermal gradient induced by laser beam combined with different cooling rates at each built layer. The SLM process parameters such as laser power, scan speed, layer thickness, hatch spacing etc have a major influence on the mechanical properties of the material fabricated. The relationship between mechanical properties associated with microstructure and process parameters is critical for the manufacture of functional components. The understanding of this relationship will help to facilitate future studies on manufacture and repair of titanium alloy parts/components with SLM technology. Increase in layer thickness will lead to increase in productivity. However, such an increase may impact on the mechanic...

Potential application and certification of laser cladding technology for repair of ageing aircraft components

In-service damage from corrosion, wear or debris impact is increasingly common with ageing military aircraft fleets. Maintenance of this type of “ageing damage” can be expensive and have significant impact on fleet availability. DSTO (Defence Science and Technology Organisation) and DMTC (Defence Materials Technology Centre) are looking at a number of surface modification/or repair technologies that can be used on an opportunity basis to restore geometry or restore the life of an aircraft component. The basis of the technology selection was that there should be low risk with the technology, and the risk is in developing an approved process for the application to aircraft. With the advent of small high-powered lasers, laser cladding (LC) is one of the surface modification technologies examined. It uses a high-powered laser beam to melt a deposited layer of material onto a substrate. Laser cladding could offer significant through-life cost savings, as a repair alternative to the replacement of damaged components. DSTO and DMTC have demonstrated that laser cladding technology could potentially be used to repair or refurbish a range of different damaged components. This paper briefly summaries the current research work on laser cladding of 7xxx series aluminum alloys and discusses potential applications and a certification path for repair of aircraft components in the near future.In-service damage from corrosion, wear or debris impact is increasingly common with ageing military aircraft fleets. Maintenance of this type of “ageing damage” can be expensive and have significant impact on fleet availability. DSTO (Defence Science and Technology Organisation) and DMTC (Defence Materials Technology Centre) are looking at a number of surface modification/or repair technologies that can be used on an opportunity basis to restore geometry or restore the life of an aircraft component. The basis of the technology selection was that there should be low risk with the technology, and the risk is in developing an approved process for the application to aircraft. With the advent of small high-powered lasers, laser cladding (LC) is one of the surface modification technologies examined. It uses a high-powered laser beam to melt a deposited layer of material onto a substrate. Laser cladding could offer significant through-life cost savings, as a repair alternative to the replacement of damaged compo...

Residual stresses in AL7075 alloy plate laser clad with AL-12Si alloy powder

Laser cladding of Al7075-T651 alloy rolled plates was performed at IRIS using a side injection powder nozzle, an Al-12Si alloy powder and a high power Nd:YAG laser. A single layer of clad alloy was deposited inside a groove machined along the plates’ rolling direction. The cladding direction was either parallel or transverse to the length of the groove, while the laser parameters (laser power, scan rate, powder mass flow rate, track increment) and size of the treated area were kept constant. Temperature measurements at the back face of the plates showed that the plates’ thermal histories differed significantly with the cladding direction. Residual stresses were measured in the clad and through the thickness of the plate using neutron diffraction scattering at ANSTO. Results are presented showing the effects of the laser cladding pattern on the energy input and the residual stress profiles in the plates.Laser cladding of Al7075-T651 alloy rolled plates was performed at IRIS using a side injection powder nozzle, an Al-12Si alloy powder and a high power Nd:YAG laser. A single layer of clad alloy was deposited inside a groove machined along the plates’ rolling direction. The cladding direction was either parallel or transverse to the length of the groove, while the laser parameters (laser power, scan rate, powder mass flow rate, track increment) and size of the treated area were kept constant. Temperature measurements at the back face of the plates showed that the plates’ thermal histories differed significantly with the cladding direction. Residual stresses were measured in the clad and through the thickness of the plate using neutron diffraction scattering at ANSTO. Results are presented showing the effects of the laser cladding pattern on the energy input and the residual stress profiles in the plates.