Study On High Qualities Fe-based Alloy For Laser Prototyping Process

Laser cladding and rapid prototyping is flexible, secure and efficient manufacturing technology that has been developed on the basis of high laser power. Most of laser cladding and laser rapid forming materials are as the same of conventional applied techniques. In order to explore the potential application value of laser surface strengthening, new kind of cladding material needs to be developed.In this paper, we developed a series of high performance Fe-based alloys used for laser rapid prototyping, which not only eliminated the crack and pore, but also improved the properties, such as tensile strength, wear resistance and hardness.Laser cladding layer without cracks that contains high carbon and boron was obtained by laser cladding of FeCrCoWCBY₂O₃ powders. The microstructure of laser cladding consists of martensite and residual austenite dendritic and interdendritic carbides. The microhardness of laser cladding increases over 3 times higher than that of substrate. The maximum of microhardness is not at the surface, but is located in 0.3 mm from the surface. The wear resistance of cladding is approximately 2 times higher than that of substrate.The coatings consisting of Fe_0.64Ni_0.36 dendrites as matrix and (Fe, Cr)₇(C, B)₃ interdendritic compounds as reinforcement were fabricated by laser cladding using Fe-based powders with different Co contents. Compared with the coatings containing 1wt.% and 5wt.% Co contents, the coating containing 3wt% Co increases by -5% in the area fraction of interdendritic regions, -55HV in the microhardness nearby the interface and -30MPa in the interfacial bond strength. The interface fracture morphology exhibits the tear appearance, which can be characterized as the ductile fracture.The structure of thin plate is composed of multilayer structure with the same features, in which every layer structure consists of parallel dendrite that is perpendicular to the base plate and the interdendritic compound. The tensile strength of cladding can reach up to the maximum values of 772.3 MPa with 4wt.% Co content as a result of Co promoting the growth of dendrite and the refinement of the interdendritic compound. However, hardness and shearing strength of the plates are decreased after heat treatment due to the decrease of solution element content. Alternatively, the hardness and strength of the plates are higher than those of 300℃ temper, which is attributed to the refinement of structure and new phase precipitation from the structure in the plate after 1050℃quenching plus 600℃tempering.The microstructure of the coating containing Y₂O₃ is finer, and the needle-like carbide is substituted for the smooth rod one. When containing 0.7wt.% Y2O3, the microhardness of coating is the highest of all (951HV), and the wear resistance is also best. The moldability of laser cladding Fe-based alloy is worse when the iron content is above 95wt.%. The wear principle of laser cladding is grain abrasion, and the wear resistance is also worse as iron content is higher.