Laser Direct Metal Deposition Technology and Microstructure and Composition Segregation of Inconel 718 Superalloy

Multilayer of laser direct metal deposition（DMD）was prepared by depositing a gas atomized pre-alloyed powder with a composition close to Inconel 718 alloy on Inconel 718 high temperature alloy substrate.The effects of the DMD parameters on the build-up rate and the structure of the deposited layer were studied.The laser DMD sample was further processed by a solution treatment.The microstructure and property of the laser DMD zone before and after heat treatment were investigated as well.The results show that the laser parameters of actual laser power of 650 W,scanning speed of 5.8 mm/s,beam diameter of 1 mm,powder feed rate of 6.45 g/min,with a corresponding specific energy of 90-130 J/mm2,can be recommended as optimum parameters for high build-up rate of Inconel 718 alloy.Under the condition of optimized parameters,a directional solidification microstructure was obtained and the average distance between the columnar crystals was 5-10 μm.The microcomposition segregation was found between the columnar crystal trunk and columnar crystal.The elements of Nb,Mo,Ti concentrated in the columnar crystal trunk.After the heat treatment,the segregation was greatly minimized,and the segregation ratios were close to 1.The hardness of the laser deposited layer did not show obvious difference along the height of the layer either for the as-deposited layer or for the heat treated layer.However,the microhardness of the laser DMD zone after heat treatment was obviously higher than that after the as-deposited treatment.During the heat treatment process,some Nb-and Mo-rich phases precipitated and strengthened DMD layer.

Effects of process parameters on surface quality,composition segregation,microstructure and properties of QSn6.5-0.1 alloy slabs fabricated by HCCM horizontal continuous casting

Columnar-grained QSn6. 5-0. 1 alloy slabs with a width of 70 mm and thickness of 10 mm were fabricated by heating-cooling combined mold（ HCCM） horizontal continuous casting. The effects of process parameters on solidification microstructure,surface quality,composition segregation and mechanical properties were studied. The results showed that the slabs with good surface quality,excellent mechanical properties and no obvious segregation could be prepared at the melt casting temperature of 1 250 ℃,the heating-mold temperature of 1 150- 1 200℃,the cooling water flow rate of 600 L / h and the casting speed of 20- 80 mm / min. The slabs had the yield strength of 124- 155 MPa,the elongation rate of 46. 6%- 56. 3% and the surface roughness of 0. 22- 0. 55μm,which enabled them to be directly processed without subsequent milling surface. The ratio of Sn content in the surface to that in the core was 0. 83- 1. 10,with an average value close to 1. 0,and not obviously influenced by process parameters. When the casting speed increased from 20 to 80 mm / min,the grain size changed little if the other process parameters were the same. When the heating-mold temperature increased from 1 150 to 1 200℃,the grain size was obviously refined and became more uniform if the casting speed was the same. Within the range of the casting speed at which the columnar grain structure could be obtained,the columnar grain size was mainly influenced by the heating-mold temperature.

Influence of heat treatments on incipient melting structures of DD5 nickel-based single crystal superalloy

The evolution of microstructure and formation mechanism of incipient melting microstructure of DD5 single crystal superalloy during solution heat treatment were studied by scanning electron microscopy(SEM),electron probe microanalysis(EPMA),and energy dispersive spectroscopy(EDS).The solidus and liquidus of single crystal alloy were obtained by differential scanning calorimetry(DSC).Results show that the mosaic-like eutectic and fan-like eutectic are dissolved at first,and the coarseγ'phase is dissolved later during the solution heat treatment of 1,390°C/2 h+1,310°C/4 h+1,320°C/10 h+air cooling(AC).The composition segregations of Al,Ta,W and Re are 0.99,0.96,1.04 and 1.16,respectively,which close to 1.The incipient melting is caused by the low local temperature of the alloy,and the micropore region with a lower melting point is the preferred position for incipient melting.

Laser Multi-layer Cladding Experiment on the DD3 Single Crystal Using FGH95 Powder:Investigation on the Microstructure of Single Crystal Cladding Layer

Laser multi\|layer cladding experiments were performed on the substrate of DD3 single crystal with FGH95 powder as cladding material.The solidification microstructure in the sample was investigated.It was found that the solidification microstructure was greatly influenced by the crystallography orientation of the substrate and the local solidification conditions.When the angle between the preferred orientation of the single crystal and the direction of heat flow in the cladding layer is less than 30°,single crystal cladding layers were acquired.Otherwise the crystallography orientation of the cladding layer will deviate from the orientation of the substrate and the microstructure with polycrystalline appears.Meanwhile,even when the experiments were performed on the same preferred crystal surface,the solidification microstructures will be different distinctly resulting from the variation of the local solidification conditions.The secondary arms were degenerated and the primary arm spacing was about 10\|20μm.Further investigation shows that the phases of the cladding layer are mainly made up ofγ,γ′,the flower\|likeγ/γ′eutectic and carbide.The morphology ofγ′was cubical and the size is less than 0.1μm.

Effects of Spiral Magnetic Field on Structures Transformation and Macrosegregation of Sn-Pb Alloy

The effect of spiral magnetic field （SMF） on the solidification process of Sn-20 wt.%Pb hypoeutectic alloy was studied in this work. The temperature distribution and the macrosegregation together with the eutectic lamellar spacing during solidification were measured under different magnetic fields. The results indicate that the compositions in the top and bottom portions of the sample are nearly the same and the segregation phenomenon is basically eliminated by SMF at an exciting current of 125 A. The morphology of the primary phase transforms from coarse dendrite to rosette or ellipsoidal equiaxed crystal and the spacing of the eutectic lamellar increases from 1.6 to 3.9 μm when the exciting current increases from 0 to 125 A. Moreover, if the exciting current is high enough, the forced fluid flow caused by SMF will enhance the process of transition from lamellar eutectic structure to anomalous rod-like one.