Research On Mechanism And Application Of Laser Cladding Forming With Wire

Laser Surface Processing(LSP)has been widely applied in the few decades.Among various techniques of LSP,laser cladding forming with wire is a surface modify technique that has demonstrated several advantages in the metallurgical field for surface repairing/ strengthening applications such as: localized heating which reduces thermal distortion and the size of the heat-affected zone,flexibility of the process,controlled levels of dilution,smooth surface finish,near isotropic mechanical properties.However,researches of laser cladding forming with wire in China started late and developed slowly which cannot catch up with international leading institutions on device development,processing research and microstructure/ property homogenization.In this study,we focused on laser cladding forming with wire technology.An internal coaxial wire feeding laser head was designed and developed,along with two experimental platform for complex laser cladding forming applications.Both 316 L and Inconel 625 wire were selected as filling materials for fundamental research of laser cladding forming with wire.Process parameters,macro morphologies,microstructures and properties of forming samples after laser cladding were investigated to verify the feasibility of laser cladding forming with wire for surface repairing/ strengthening applications.In addition,samples for surface repairing/ strengthening applications were successfully fabricated on the surface of 316 L stainless steel with optimized process parameters by laser cladding forming with wire,providing theoretical foundation and engineering experience for practical application.The main results obtained in this study are summarized as follows.(1)The laser cladding experimental platform based on paraxial wire feeding were first constructed first for fundamental research.An internal coaxial wire feeding laser head with a four light spit system was also designed and developed based on the research experiences abroad after optical path design and equipment upgrading for high accuracy,high efficiency and multi direction cladding requirements.The laser cladding experimental platform based on coaxial wire feeding were also constructed including the coaxial wire feeding laser head.(2)Samples cladded using 316 L stainless steel wire were successfully fabricated on a 316 L stainless steel surface under optimized conditions.The results showed that satisfactory samples with large deposition heights and smooth surfaces could be achieved under appropriate parameters of lower heat input and larger wire feed rate.The uniform structures had fine cellular and network austenite grains with good metallurgical bonding between layers,showing an austenite solidification mode.Precipitated ferrite at the grain boundaries showed a subgrain structure with fine uniform grain size.High microhardness(205–226 HV)and tensile strength(669 MPa)were detected of typical samples,indicating excellent mechanical properties.(3)For surface modification industry,Inconel 625 alloy was utilized extensively as a coating material due to its excellent corrosion and oxidation resistance,as well as its good intersolubility with iron.Samples cladded using Inconel 625 wire were successfully fabricated on a 316 L stainless steel surface under optimized conditions.The results indicated that the defect-free Inconel 625 samples presented an obvious microstructure transformation while the bonding interface can be divided into three different areas of forming area,bonding area and substrate area.The forming area was consist of partial uniform refined austenite grains with various formations.An unmixed area was observed near the bonding interface with precipitated ferrite of different formations.A decrease of the hardness(H)and reduced elastic modulus(Er)profile was detected in this area.Forming area and bonding area exhibited superior tensile properties at both room temperature and high temperature than substrate.The corrosion performance of forming area was also close to bonding area and superior to substrate in different solutions,indicating an excellent protecting effect of Inconel 625 forming samples.(4)Samples cladded using Inconel 625 wire and reinforced by titanium carbide(Ti C)particles were successfully fabricated on a 316 L stainless steel surface under optimized conditions.The results showed that homogeneous distributed Ti C particles,along with refined microstructures were obtained in Ti C reinforced Inconel 625 composite samples under appropriate process parameters of higher heat input and smaller wire feed rate.During laser cladding forming,almost no transformation of Fe or Ni was occurred around the Ti C particle but Laves phases were precipitated at the boundary.Compared with the pure Inconel 625 samples,significantly improvement of microhardness and tensile strength were observed in Ti C reinforced Inconel 625 samples.The Ti C reinforced Inconel 625 samples also exhibited good corrosion resistance,proving a further surface improvement effect.(5)Application tests of laser cladding forming with wire were carried out using the laser cladding experimental platform based on coaxial wire feeding.The 50-layer forming sample,40-layer arc forming sample and 5×5 block forming sample cladded using 316 L stainless steel wire were successfully fabricated on a 316 L stainless steel surface under optimized conditions.All these sample exhibited entire structures,smooth surfaces and uniform refined microstructures.The experiment verify the feasibility of laser cladding forming with wire for surface repairing applications using the same filling material.In addition,the single-layer and multi-channel Inconel 625 reinforced forming samples were also fabricated on a 316 L stainless steel surface under optimized conditions,showing good metallurgical integration with substrate without defects.The experiment verify the feasibility of laser cladding forming with wire for surface strengthening applications using Inconel 625 alloy.