Preparation And Investigation On Microstructures And Properties Of Ni-Base Quasi-K445 Superalloy

As superalloys have better combination of higher strength at elevated temperature, better oxidation resistance and corrosion resistance, better fatigue resistance, fracture toughness and plasticity, etc, they are irreplaceable materials for aero-engine, rocket engine and high temperature parts of gas turbine, and they are also widely used in the civil industry, such as atomic energy, communications and transport, petrochemical engineering, etc. With the development of gas turbine engine, the increasingly severe requirements are put forward for the properties of superalloys, it is very important for melting mean selection to optimize microstructure and improve properties. By means of vacuum melting, as-cast Ni-base quasi-K445 superalloys with different melting processes and different raw powder materials and bar materials were prepared. Meanwhile, the characteristics of the microstructure of the new superalloy as well as the effect of processing parameters and raw materials on the microstructure and properties of Ni-base quasi-K445 superalloy were studied. The following conclusions can be drawn from those investigations:1. The as-cast microstructure of the new Ni-base quasi-K445 superalloy consists of dendriticγmatrix, dispersedγ′phase and mushroom-like or sunflower-like eutectic (γ+γ′), big flake or fishbone-likeγ′′, blocky MC carbides, banding or skeletal M3B2 borides on grain boundary and in interdendritic regions.2. As melting temperature increases from 1450℃to 1600℃with 50℃interval, the dimesnsion of dendrites in quasi-K445 superalloy gradually decreases,the amount of eutectic (γ+γ′) andγ′′distributing in interdendritic regions increases and the amount and dimension of MC carbides decrease. At 1600℃, the superalloy has the most uniform microstructure, the finest dendrites, the largest amount of eutecticγ′andγ′′and the least amount of MC.3. With the increase of melting temperature, the hardness of quasi-K445 increases. At the1600℃melting temperature, the hardness can reach maximum HB384. The distribution of measured hardness values is narrower, and macrosegregation of the superalloy has alleviated.4. As the holding time is held for 15mins, 30mins, 60mins, 90mins and 120mins respectively at 1500℃, the dimension of dendrites as well as the amount of MC in quasi-K445 superalloy firstly decrease then increase.On the contrary, the amount of eutectic (γ+γ′) andγ′′firstly increase then decrease. When the holding time is 30mins, the alloy has the most uniform microstructure with the finest dendrites, the biggest amounts of eutecticγ′andγ′′and the least amoun of MC.5. With the increase of holding time, the hardness of quasi-K445 superalloy firstly increases then decreases, and the macrosegregation firstly alleviates then aggravates. At the holding time of 30mins, the hardness of the superalloy reaches the maxium HB381, the measured hardness is more close to the average value with smaller deviation and the degree of macrosegregation is the least.6. Quasi-K445 superalloys were prepared with Ni powder and Ni bars respectively under three melting conditions of holding for 90min at 1450℃, holding for 30min at 1500℃and holding for 90min at 1500℃. The effect of raw materials on the phase distribution, size and properties under the above melting conditions has some difference on some degree.As a whole, Ni powder is more propitious to the but the microstructure and properties of the superalloys,but melting process has more obivious effect.