Formation mechanism and wear behavior of gradient nanostructured Inconel 625 alloy

The formation mechanism and wear behavior of a gradient nanostructured(GNS) Inconel 625 alloy were investigated using SEM, TEM and ball-on-disc sliding wear tester. The results show that surface mechanical grinding treatment(SMGT) induced an approximately 800 μm-deep gradient microstructure, consisting of surface nano-grained,nano-laminated, nano-twined, and severely deformed layers, which resulted in a reduced gradient in micro-hardness from 6.95 GPa(topmost surface) to 2.77 GPa(coarse-grained matrix). The nano-grained layer resulted from the formation of high-density nano-twins and subsequent interaction between nano-twins and dislocations. The width and depth of the wear scar, wear loss volume, and wear rate of the SMGT-treated sample were smaller than those of untreated coarse-grained sample. Moreover, the wear mechanisms for both samples were mainly abrasive wear and adhesive wear, accompanied with mild oxidation wear. The notable wear resistance enhancement of the GNS Inconel 625 alloy was attributed to the high micro-hardness, high residual compressive stress, and high strain capacity of the GNS surface layer.

Precipitation Study in Inconel 625 Alloy by Positron Annihilation Spectroscopy

Precipitation in Inconel 625 alloy has been studied by positron annihilation spectroscopy and electron microscopy. The observed dependence of annihilation characteristics on aging time is attributed to the change of the positron state due to the increase and decrease of the density and size of the 7' precipitates. Hardness measurements and lifetime measurements are in good agreement.

Effects of Heating and Hot Extrusion Process on Microstructure and Properties of Inconel 625 Alloy

The effects of the heating process and hot extrusion on the microstructure and properties of inconel 625 alloy were studied. The experimental results showed that the properties of Inconel 625 alloy could be improved through the heating process and hot extrusion concomitant with a reduced corrosion rate. The M23C6 carbide, generated in the heating process, was retained and distributed at the grain boundary during the process of hot extrusion, which had an important influence on both elongation and corrosion resistance. The improvement of the comprehensive properties of the material, as measured by a tensile test at room temperature, was correlated with the dissolution of segregation Nb. A typical ductile fracture changed to a cleavage fracture where secondary cracks could be clearly seen. With the increase of the extrusion ratio, the real extrusion temperature was higher, which led to more dissolution of the M23C6 carbide, decreased the number of secondary cracks, enhanced the effect of solid solution strengthening, and reduced the intergranular corrosion rate. Under the condition of a high extrusion ratio and a high extrusion speed, the less extrusion time made it possible to obtain organization with a smaller average grain size. Moreover, in this case, the M23C6 carbide and segregated Nb did not have enough time to diffuse. Thus all samples exhibited medium strengths and corrosion rates after extrusion.

亚/超临界水-磷酸盐环境中Alloy625的腐蚀行为研究

腐蚀问题限制了亚/超临界水氧化技术的发展,而磷酸盐在超临界水环境中会形成低熔点混合熔盐,形成更严峻的腐蚀环境,如何解决腐蚀和盐沉积问题成为了目前研究的重点。采用失重法、X射线衍射(XRD)、能谱(EDS)和扫描电镜(SEM)研究Alloy625在亚/超临界水-磷酸盐环境中的腐蚀行为,重点考察了表面形貌和腐蚀产物的演变特征。结果表明,腐蚀产物除金属磷酸盐外,在亚临界条件中主要为Cr_(2)O_(3)、NiO、FeO和NiCr_(2)O_(4),在超临界条件下腐蚀产物膜内层由致密的鳞片状Ni_(2)O_(3)、Cr_(2)O_(3)和NiCr_(2)O_(4)尖晶石构成,外层由疏松的针状Fe_(2)O_(3)和FePO_(4)构成。此外,磷酸盐能引起氧化膜严重剥落,使腐蚀加剧,在350℃亚临界条件下腐蚀失重规律呈类抛物线,而在450℃超临界中腐蚀失重受腐蚀产物膜演化过程(生成-脱落-再生成)的影响,腐蚀质量变化远高于亚临界条件下的。

Influence of processing parameters on deposition characteristics of Inconel 625 superalloy fabricated by laser solid forming

A series of single track clads of Inconel 625 alloy were fabricated by laser solid forming.To achieve the high dimensional accuracy and excellent mechanical properties,the effect of processing parameters on the geometry,the formation of Laves phase and the residual stress was investigated.The results show that laser power and scanning speed had a dramatical influence on the width and height of single-track clads.According to the columnar to equiaxed transition curve of Inconel 625,the grain morphology can be predicted during the LSF process.With the increasing laser power and the decreasing scanning speed,the segregation degree of Si,Nb,Mo,the volume fraction and size of Laves phase increased.Vickers indentation was used to demonstrate that optimizing processing parameter can achieve the minimum residual tensile stress.

Effects of solution treatment on microstructure and tensile properties of as-cast alloy 625

Effects of solution treatment between 1050 and 1250℃on microstructure and tensile properties of as-cast alloy 625 were investigated.The microstructure and solidification characteristics of the alloy were studied by SEM,EDS,EPMA and DTA.The results showed that the solidification sequence of the alloy should be written as L→L+γ→L+γ+MC→L+γ+MC+γ/Laves→γ+MC+γ/Laves.After solution treatment at 1225 and 1250°C,incipient melting of Laves phase was observed.The ultimate tensile strength decreased monotonically with the increase of solution treatment temperature,and the yield strength had no significant variation.The elongation increased slightly at first and then reached a minimum value at 1250°C.The fracture mechanism changed from transgranular mode to intergranular mode after solution at 1250°C for the reason that numerous Laves phases melted at grain boundaries and microcracks nucleated in the molten pool.The suitable solution treatment temperature of this alloy was 1200°C.

Alloy625镍基合金管板的加工与检验

介绍了对Alloy 625材料的加工试验及UNS NO6625合金管板的加工,为同类产品的制造积累了经验。

DRX rules during extrusion process of large-scale thick-walled Inconel 625 pipe by FE method

A thermal-mechanical and micro-macro coupled finite element（FE） model for the hot extrusion process of large-scale thick-walled Inconel 625 pipe was developed based on the DEFORM-2D platform.Then,the influence rules of the key extrusion parameters on the average grain size and grain uniformity of the extruded pipe were revealed.The results show that with the increase of initial billet temperature,extrusion speed and friction coefficient,the grain uniformity is firstly improved and then deteriorated.Larger extrusion ratio leads to more uniform grain distribution.With the increase of initial billet temperature,the average grain size of the pipe first decreases and then increases.Additionally,larger extrusion ratio can bring smaller average grain size.The extrusion speed and friction coefficient have slight effects on the average grain size of the extruded pipe.

Prediction of fracture limits of Ni-Cr based alloy under warm forming condition using ductile damage models and numerical method

The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit diagram(FFLD)was transformed into a stress-based(σ-FFLD)and effective plastic strain(EPS)vs triaxiality(η)plot to remove the excess dependency of fracture limits over the strains.For the prediction of fracture limits,seven different damage models were calibrated.The Oh model displayed the best ability to predict the fracture locus with the least absolute error.Though the experimentally obtained fracture limits have only been used for the numerical analysis,none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality(0.33<η<0.66).The deep drawing process window helped to determine wrinkling,safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions.Further,the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition.All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.

Phase Transformation Strengthening of Hot Extruded Inconel 625 under High-temperature Load Environment

Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy exhibits an excellent creep resistance at 700 ℃ and below. When the creep temperature rises to 750 ℃, the creep resistance falls drastically due to the failure of phase transformation strengthening and the precipitation of a large amount of δ phase and σ phase at the grain boundary. The special temperature-sensitive characteristics of Inconel 625 alloy play a very important role in its fracture. When the strain rate is 8.33×10^-3s^-1, the strength of the specimen is higher than that of other parameters attributed to the effect of phase transformation strengthening. With the increase of Ni3(Al, Ti), the phase transformation strengthening inhibits thickening of the stacking faults into twins and improves the overall mechanical properties of the alloy. With the increase of the aging time, the granular Cr-rich M23C6 carbides continue to precipitate at the grain boundary, which hinders the movement of the dislocations and obviously increases the strength of the samples. Especially, the yield strength increases several times.

Mechanism of high temperature oxidation of Inconel 625 superalloy with various solution and ageing heat treatment processes

The high-temperature oxidation behaviour of the Inconel 625 alloy at 950℃ was investigated after different ageing treatments.The effect of heat treatment on the oxidation behaviour of the alloy was analysed by characterizing the structure and elemental distribution before and after oxidation.The results reveal that the two ageing treatments at 650℃ for 500 h and at 750℃ for 400 h both reduced the oxidation mass gain.After oxidation at 950℃,an outer Cr_(2)O_(3) layer and inner Al_(2)O_(3) are identified as the main oxidation products.Moreover,Nb_(2)O_(5) andδ(Ni_(3)Nb)phases precipitated after oxidation.The ageing treatments cause the rapid generation of a dense Cr_(2)O_(3) layer on the surface,which prevents the diffusion of oxygen into the matrix,reduce the Al_(2)O_(3) inward growth depth,and improve the oxidation resistance of the alloy.

NICKEL-BASE ALLOY SHEET ALLOYS USED IN AEROSPACE APPLICATIONS

Many gas turbine components are made from nickel alloy sheet. Most are used for directing or containing gases at high temperatures and pressures where metal temperatures can be as high as 1090℃ (2000°F). These applications included combustor systems, casings and liners, transition and exhaust ducting, afterburners, and thrust reversere. Light weight components and sub-assemblies call for alloy sheet with high levels of stength and oxidation resistance. Complex component design calls for excellent ductility and ease of fabrication.The wide range of nickel alloy sheet alloys presently used in aircraft and land-based gas turbines is briefly described and typical properties presented. New sheet alloy developments, involving INCONEL￣* alloys 625LCF, 718SPF and MA754, are presented including the process routes involved and material properties.

Grain Growth Behavior of Inconel 625 Superalloy

The grain growth（GG）behavior of Inconel 625 superalloy was studied in the temperature range of 900-1 250 ℃and holding time range of 10-80 min.Microstructures of the alloy were characterized by optical metallography,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.Grains grew obviously with either increasing temperature or extending holding time at temperatures above 1 050℃.However,at temperatures lower than 1 050 ℃,the GG was sluggish due to the pinning effect of carbide particles on grain boundary（GB）.Threshold temperature for transition from mixed grain structure to uniform one was considered to be around 1 100℃.Once the temperatures surpassed 1 200℃,an instant increase in the grain size occurred showing no dependence on holding time.TEM analysis showed that the dominant second phase formed heterogeneously on the GB was M6 C,which significantly impeded grain growth.On the basis of experimental data,the mathematical model of GG was established,which can describe GG behavior of Inconel 625 alloy during solution treatment（ST）at 1 100-1 250 ℃.The activation energy for GG of Inconel 625 alloy was 207.3kJ,which suggested that the GG of Inconel 625 alloy was controlled by the process of GB diffusion.

厚壁Alloy 625接管现场组对焊接工艺

介绍了厚壁Alloy 625接管现场组对焊接过程和特点,阐述了现场组对的难点及解决方案,厚壁Alloy 625接管焊接过程的控制要点,为以后厚壁Alloy 625接管的现场组对、焊接积累了经验。