High temperature alloys pdf

For this reason, it is appropriate to preoxidize the components. Regarding the literature [] the preoxidation of some alloys has proved to be beneficial for high temperature applications. However, most widely used materials in aggressive high temperature enviroments are Nickel-based alloys, when wear resistance combined with oxidation or hot corrosion is required [5]. In most cases the base materials are coated with a protective layer.

Self Fluxing alloys like Ni-Cr-B-Si are also used to protect steels or Ni-base materials for applications at room- or high temperature. However, the literature does not give enough informations about the thermocyclic oxidation behaviour of Ni-Cr-B-Si alloys. Ramesh and co-workers [5]. The holding time in the furnace was 1 h and the cooling time amounted 20 min. The oxide scale formed on the surfaces of all the NiCrFeSiB-coated steels was found to be compact and adherent. No peaks for SiO2 were present.

The uncoated steels showed Fe2O3 as the major peaks. Above all, no spallation of scale was observed. This is a prerequisite for the protection against above described external influences. The specimens were degreased in acetone and dried in hot air before testing. The exposure time in the furnace was 30 min, the cooling time amounted 5 min. Nominal chemical composition of the used specimens wt. The research results have confirmed the known theory, that the diffusion rate in grain boundaries is much higher in comparison with the volume diffusion.

The presence of cracks in this area confirms the high oxidation growth rate which induces a high degree of residual stresses followed inevitably by crack evolution. The high temperature resistance, corrosion resistance and other properties of superalloys mainly depend on its chemical composition and organizational structure. Taking GH nickel-base deformed superalloy as an example, it can be seen that the niobium content in GH alloy is high, and the degree of niobium segregation in the alloy is directly related to the metallurgical process.

The chemical elements and matrix structure of GH alloy show its strong mechanical properties. Yield strength and tensile strength are several times better than 45 steel, and plasticity is also better than 45 steel.

The stable lattice structure and a large number of strengthening factors construct its excellent mechanical properties. Due to its complex and harsh working environment, the integrity of the processed surface of superalloys plays a very important role in the performance of its performance. However, superalloy is a typical difficult-to-machine material.

Its micro-strengthening item has high hardness, severe work hardening, and it has high shear stress resistance and low thermal conductivity. The cutting force and cutting temperature in the cutting area are high, which often occurs during processing. The quality of the machined surface is low, and the tool breakage is very serious.

Under general cutting conditions, the surface layer of the superalloy will produce excessive problems such as hardened layer, residual stress, white layer, black layer, and grain deformation layer. The traditional classification of superalloy materials can be carried out according to the following three methods: according to the type of matrix element, alloy strengthening type, and material forming method. Iron-based superalloys can also be called heat-resistant alloy steels. The solid solution and aging process can greatly improve the creep resistance and compressive yield strength.

In terms of high-temperature alloys used in high-temperature environments, the use of nickel-based superalloys far exceeds the use of iron-based and cobalt-based superalloys.

At the same time, nickel-based superalloys are also the largest and most used superalloy in my country. Many turbine blades and combustion chambers of turbine engines, and even turbochargers also use nickel-based alloys as preparation materials. It should be said that this huge improvement has also prompted the casting process and surface coating. Rapid development in other areas.

At the same time, elements such as Cr and Ni need to be added to improve the heat resistance of the superalloy. Although this superalloy has better heat resistance, it is due to various countries The output of cobalt resources is relatively small and the processing is relatively difficult, so the amount of cobalt resources is not large.

In order to obtain better heat resistance, under normal conditions, elements such as W, MO, Ti, Al, Co should be added during preparation to ensure its superior thermal fatigue resistance. According to the type of alloy strengthening, superalloys can be divided into solid solution strengthened superalloys and aging precipitation strengthened alloys.

The so-called solid solution strengthening type means adding some alloying elements to iron, nickel or cobalt-based superalloys to form a single-phase austenite structure. The solute atoms deform the solid solution matrix lattice and increase the sliding resistance in the solid solution for strengthening. Some solute atoms can reduce the stacking fault energy of the alloy system and increase the tendency of dislocation decomposition, making it difficult for cross-slip to proceed, and the alloy is strengthened to achieve the purpose of strengthening the superalloy.

The so-called aging precipitation strengthening refers to a heat treatment process in which the alloy workpiece is solid-solution treated and cold plastically deformed, and then placed at a higher temperature or at room temperature to maintain its performance.

Divided by material forming methods: casting superalloys including ordinary casting alloys, single crystal alloys, oriented alloys, etc. The alloy material that uses the casting method to directly prepare the parts is called the casting superalloy. According to the composition of the alloy matrix, it can be divided into three types: iron-based casting superalloys, nickel-based casting superalloys and drill-based casting superalloys.

According to the crystallization method, it can be divided into four types: polycrystalline casting superalloys, directional solidification casting superalloys, directional eutectic casting superalloys and single crystal casting superalloys.

It is still the most used material in aero-engines and is widely used at home and abroad. Take GH alloy as an example, it is one of the main varieties with the most applications at home and abroad. In my country, the bolts, compressors, wheels, and oil slingers of turboshaft engines are mainly used as main parts. With the maturity of other alloy products, the use of deformed superalloys may gradually decrease, but it will still be in the next few decades.

Including powder superalloys, titanium-aluminum intermetallic compounds, oxide dispersion-strengthened superalloys, corrosion-resistant superalloys, powder metallurgy and nano-materials and other subdivided product fields.

GH alloy is a nickel-chromium-iron-based high-temperature alloy. GH alloy is a nickel-based deformed high-temperature alloy. Nickel-based alloys are one of the most complex alloys. It is widely used in the manufacture of various high-temperature components.

At the same time, it is also the most eye-catching alloy among all high-temperature alloys. Its relative service temperature is also the highest among all common alloy series.

It was an age-hardening nickel-chromium-iron-based deformation alloy that was publicly introduced in A wide range of superalloys. Due to the good comprehensive performance of GH, it is widely used in aero-engine compressor discs, compressor shafts, compressor blades, turbine discs, turbine shafts, casings, fasteners and other structural parts and plates Welding parts, etc.

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