Cyclic Oxidation Resistance of In718 Superalloy Treated by Laser Peening

The aim of this study was to improve the cyclic oxidation resistance of In718 superalloy by laser peening（LP）. Specimens were treated by LP from one to three times, respectively. The cyclic oxidation tests at 900 ℃ for periods up to 2 h were conducted. Changes of the top surface morphology and microstructure were analyzed by scanning electron microscope （SEM）, energy-dispersive spectra （EDS）, transmission electron microscope （TEM） and X-ray diffraction technique （XRD）, respectively. The weights were measured between the oxidation cycles to assess the oxidation of the specimens. The top surface microstructure after LP was characterized by highly tangled and dense dislocation arrangements and a high amount of twins. Protective oxidation layer was generated more quickly on the surface treated by LP. The average oxidation rate was about 50 % lower. A tiny homogeneous oxidation layer containing （Fe,Cr）2O3, NiCrO3 and Ni（A1,Cr）2O4 spinel was generated on the surface. The experimental results of cyclic oxidation tests show that specimens treated by LP have a better high temperature oxidation resistance, and the antistrip performance of the oxidation layer improves. Moreover, the effects of LP are strengthened with the increase of laser peening.

Cyclic Oxidation Resistance of a Sputtered Micro-grained Superalloy Film

The cyclic oxidation resistance of cast Ni-base superalloy K38G and its sputtered micro-grained film were studied between 950℃ and room temper- ature in air.The results show that the weight gain of micrograined films is much less than that of cast al- loy during cyclic oxidation,and the resistance of micro-grained fihns is even better than that of the aluminide coating on the same alloy.On the surface of cast alloy K38G,complex oxide scales of Cr_2O_3, TiO_2 and NiCr_2O_4 spinel formed and they began to spall alter about 30 cycles of test.However,on the micro-grained films,continuous and thin α-Al_2O_2 scale was formed and did not spall throughout the cyclic oxidation test.

Influence of prior cyclic oxidation on high temperature low cycle fatigue life of bare and Pt-Al coated superalloy Rene®80

The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces has an effective role in the fatigue strength and ductility of the alloys.In the present work,the effect of prior cyclic oxidation on the high temperature low cycle fatigue(HTLCF)properties of nickel-based superalloy Rene®80 has been assessed in the uncoated state and in the Pt-aluminide(Pt-Al)coated condition at 930℃.To apply cyclic oxidation,simulation of engine thermal exposure was carried out by exposing coated and uncoated fatigue specimens in the burner rig(120 cycles at 1100℃).The cyclic oxidation procedure led to a changing in the coating microstructure from the dual-phase(ξ-PtAl_(2)+β-(Ni,Pt)Al)to single phase(β-(Ni,Pt)Al).Results of HTLCF tests showed an improvement in the HTLCF life around 11.5%in the unexposed coated specimen(pre-cyclic oxidation)as compared to unexposed bare specimen,while this rise for exposed coated specimen(post-cyclic oxidation)was only 5%.Although a mixed mode fracture morphology(ductile and brittle)was observed on the fracture surfaces of failed specimens,the wider regions of brittle fracture belonged to exposed coated/uncoated ones.

Improving cyclic oxidation resistance of Ni_(3)Al-based single crystal superalloy with low-diffusion platinum-modified aluminide coating

A low-diffusion Ni Re Pt Al coating((Ni,Pt)Al outer layer in addition to a Re-rich diffusion barrier layer)was prepared on a Ni_(3)Al-base single crystal(SC)superalloy via electroplating and gaseous aluminizing treatments,wherein the electroplating procedures consisted of the composite deposition of Ni-Re followed by electroplating of Pt.In order to perform a comparison with conventional Ni Al and(Ni,Pt)Al coatings,the cyclic oxidation performance of the Ni Re Pt Al coating was evaluated at 1100 and 1150℃.We observed that the oxidation resistance of the Ni Re Pt Al coating was significantly improved by the greater presence of the residualβ-Ni Al phase in the outer layer and the lesser outward-diffusion of Mo from the substrate.In addition,the coating with the Re-rich diffusion barrier demonstrated a lower extent of interdiffusion into the substrate,where the thickness of the second reaction zone(SRZ)in the substrate alloy decreased by 25%.The mechanisms responsible for improving the oxidation resistance and decreasing the extent of SRZ formation are discussed,in which a particular attention is paid to the inhibition of the outward diffusion of Mo by the Re-based diffusion barrier.

Microstructural evolution and mechanical properties of NiCrAlYSi+NiAl/cBN abrasive coating coated superalloy during cyclic oxidation

Cyclic oxidation behavior of Ni Cr Al YSi+Ni Al/c BN abrasive coating at 900°C and the mechanical properties of the coating-substrate system were investigated.Results indicated that elemental interdiffusion occurred between the coating and substrate,which caused the formation of interdiffusion zone(IDZ)and secondary reaction zone(SRZ)during aluminization,while their compositions and structures changed with oxidation.Al N interfacial layer formed at c BN/metallic matrix interface during aluminization,while it transformed into multilayer oxides during oxidation.Due to the microstructural evolution of these interfaces,the fracture behavior and bending toughness of the system changed greatly during three-point bending tests.Besides,the damage mechanisms were discussed.

The Intrinsic Relationship Between Microstructure Evolution and Thermal Fatigue Behavior of a Single-Crystal Cobalt-Base Superalloy

The intrinsic relationship between the microstructure evolution and thermal fatigue behavior of a single-crystal cobalt-base superalloy has been investigated. The thermal fatigue tests are performed cyclically between room temperature and 1050 ℃ using V-notch plate specimens. Three states of thermal fatigue specimens are selected： the as-cast, solutionized as well as aged states. The solution treatment is carried out at 1260 ℃ for 24 h, which results in the dissolution of most of interdendritic continuous primary carbides. The subsequent aging treatment is carried out at 1100 ℃ for 100 h after solution treatment, resulting in the precipitation of a profusion of chain- and point-like M23C6 carbides in the matrix. The results indicate that the heat treatment can improve the thermal fatigue properties of the alloy and the effect of the solution treatment is more prominent than that of the aging treatment. The coarse and continuously distributed primary carbides in the as-cast state are changed into small and discontinuous distribution by heat treatment, which is the dominant factor in the improvement of thermal fatigue property. Additionally, the effect of oxidation behavior during thermal fatigue test on the thermal fatigue behavior is also studied.

Influence of cyclic frequency on oxidation behavior of K38 superalloy with yttrium additions at 1273 K

Cyclic oxidation test is a fundamental method to assess lifetime of materials in high temperature environment.Cycle length or cyclic frequency is one important variable in cyclic oxidation testing.In present work,cyclic oxidation tests were performed on cast K38 alloys with 0 wt.%,0.1 wt.%,and 0.5 wt.% yttrium additions at 1 273 K respectively.Two cyclic frequencies were used to investigate the influence of cycle length （1 h vs.20 h） on the high temperature oxidation behavior of superalloy.The results showed that the degradation of cast K38 alloy critically was dependent on the cyclic frequency.The yttrium addition was beneficial to reducing scale-growth rate,improving the scale adhesion and stress releasing,thereby increased the spallation resistance.It could be drawn that the effect of cyclic frequency was highly dependent on the scale adherence to the substrate.

镍基单晶合金高温氧化的动力学特征

通过对镍基单晶合金高温氧比后的组织结构观察和内氧比层深与循环氧比质量变比动力学曲线 的测定．研究了合金的高温氧比特性，结果表明：在大气环境条件下．无保护涂层合金发生明显的氧比和内氧化：在近异形大颗粒内氧比物处出现贫Ａｌ区．使区内γ’强比相消失：内氧比层的深度随时间的变比服 从抛物线规律．外加拉伸应力使内氧比加剧，在循环氧比初期， 由于形成以Ａｌ为主的氧化膜易剥落．质量 变比动力学曲线表现出较快的减重趋势：合金在２０～８０ ｈ的循环氧比期间，在１０４０℃和１０７０℃分别 呈较缓的增、减重趋势。

钴基高温合金的循环氧化行为研究

研究了钴基高温合金K40S在 95 0℃和 10 0 0℃的循环氧化行为 .发现合金在 95 0℃ 40 0h以内的抗循环氧化性能较好 .合金在 10 0 0℃氧化 5 0h以后因为表面氧化膜剥落开始出现失重现象 .在 10 0 0℃循环氧化初期的产物主要为Cr2 O3 ,其次为CoCr2 O4 和少量的CoO ,40 0h以后 ,Cr2 O3 基本剥落 ,合金表面由于Cr的损耗又生成Cr2 WO6、NiCr2 O4 以及挥发性的WO3 氧化产物 .添加Si和Mn元素使K40S合金抗循环氧化性能明显地比不含Si和Mn元素的DZ40M钴基高温合金优越 .

NiCoCrAlYSi涂层对镍基单晶合金高温氧化特性的影响

通过对有/无NiCoCrAlYSi涂层镍基单晶合金高温氧化后的组织结构观察与分析、及等温循环氧化质量变化动力学曲线测定,研究了有/无涂层合金的高温氧化特性。结果表明:在高温氧化期间,无涂层合金表层发生明显的氧化和内氧化,在异形大颗粒内氧化物附近出现贫Al区,使区内γ′相消失;元素贫化区尺寸随时间的变化服从抛物线规律;无涂层合金经不同温度循环氧化具有不同的动力学特征,1040℃循环氧化表现的较大增减重波动幅度的原因是元素Al和Cr的交替选择性氧化;涂层合金经不同温度循环氧化后无明显失重特征,该涂层可有效改善合金的抗氧化性能。

盐雾腐蚀对热障涂层高温循环氧化性能的影响

利用电子束物理气相沉积法在Ni基高温合金表面制备了(ZrO2+MCrAlY)双层结构热障涂层。研究了常温盐雾腐蚀对其循环氧化行为的影响。试验结果表明涂层经过常温盐雾腐蚀后,陶瓷层的裂纹发生扩展,氧化锆晶体挤压、变形,同时由于常温盐雾环境的作用导致涂层在高温氧化过程中粘结层氧化严重,生成的热生长氧化层产生较大的体积膨胀效应,导致应力集中,降低了涂层的高温循环氧化性能,缩短了涂层的寿命。

溅射纳米晶IN738合金涂层的抗循环氧化行为

研究了高温合金ＩＮ７３８及其溅射纳米晶涂层的抗循环氧化行为,结果表明:纳米晶涂层在９５０℃的抗循环氧化性能比铸态合金好,纳米晶涂层氧化时形成双层的外氧化膜,其内层为连续的Ａｌ２Ｏ３氧化层,具有较好的保护性和粘附性,提高了合金抗循环氧化性能。

LDZ125微晶涂层抗循环氧化性能

研究了高温合金ＬＤＺ１２５及其溅射微晶涂层的抗循环氧化行为．微晶涂层仅由γ相组成，晶粒尺寸约为３０ｎｍ．结果表明：微晶涂层在１０００℃的抗循环氧化性能比铸态合金的有极大提高．微晶层氧化时只形成单一的Ａｌ２Ｏ３氧化膜，且在整个氧化过程中未见开裂剥落，有极好的粘附性．

含铼镍基单晶高温合金在900℃的循环氧化行为

采用X射线衍射(XRD),扫描电镜(SEM)及能谱(EDAX)等手段,研究了一种含铼镍基单晶高温合金在900℃的高温循环氧化行为。结果表明,在氧化初期合金的氧化质量增加较快,随着氧化时间延长氧化增重和失重交替进行,氧化动力学曲线不符合抛物线规律。高温氧化期间,合金发生明显的外氧化和内氧化,900℃氧化形成的氧化膜由三层组成,外层氧化膜由NiO、Al2O3和(Ni,Co)Cr2O4组成;中间层为平直的CrTaO4及AlTaO4层;内层氧化物为Al2O3。在合金的氧化期间,分布在中间层的富Re、Ta和W相可抑制基体中Al向外扩散,并抑制氧化膜的生长,使氧化速度降低。

NiCr-CrAl涂层的高温氧化行为

采用固体粉末包埋法在高温合金K438表面制备了一种NiZr-CrAl涂层和单渗铝涂层,通过循环氧化动力学曲线分析、形貌观察及物相分析等对比研究了两种涂层在1000℃下的循环氧化行为。结果表明:单渗铝涂层和NiCr-CrAl涂层均由β-NiAl构成;在循环氧化300h后,NiCr-CrAl涂层质量增加明显低于单渗铝涂层的;单渗铝涂层表面氧化物由α-Al2O3、NiAl2O4和TiO2混合氧化物组成,涂层出现了明显的NiAl向Ni3Al退化,涂层抗氧化性能下降;而NiCrCrAl涂层表面氧化物仍由致密的α-Al2O3相构成,涂层中仅出现轻微的退化,表现出优异的抗循环氧化性能。

K52高温合金及其溅射涂层的循环氧化行为研究

利用磁控溅射的方法在K52高温合金上制备同成分的纳米晶涂层,研究了该合金及纳米晶涂层在900℃的循环氧化行为。结果表明:铸态合金在循环氧化过程中表面有剥落现象,生成了疏松的Cr2O3和TiO2混合氧化膜;而溅射涂层则生成了单一致密的-αAl2O3膜,没有出现剥落现象,提高了合金的抗高温腐蚀性能。讨论了合金及其纳米晶涂层的氧化机理。

不同渗铝工艺对铂铝涂层循环氧化性能影响研究

为了促进国产商用CJ-1000预研发动机涡轮工作叶片的顺利研发,针对第二代镍基单晶高温合金N5,采用电镀铂和气相渗铝工艺,制备铂铝涂层,并考察涂层的高温氧化性能,评价涂层服役过程中组织结构变化及其退化机制。通过对比1080℃5 h渗铝处理和1100℃4 h渗铝处理的涂层在1100℃下的循环氧化行为及组织结构变化,发现1080℃5 h渗铝的涂层具有更好的抗剥落能力,其抗高温氧化性能好于1100℃4 h渗铝样品。

两种MCrAlY涂层/DD6合金的循环氧化和互扩散行为

在DD6单晶高温合金基体上,利用电子束物理气相沉积(EB-PVD)技术制备Ni Co Cr Al Y涂层,采用低压等离子喷涂(LPPS)技术制备Ni Co Cr Al YHf Si涂层,通过扫描电镜(SEM)、X射线能谱(EDS)、X射线衍射(XRD)、电子探针显微分析(EPMA)等手段研究了在1100℃下的热循环氧化和互扩散行为。结果表明,涂层显著提高了DD6基体的抗氧化能力,经100h的循环氧化后,涂层表面氧化层主要成分仍为α-Al2O3,依然发挥着较好的抗氧化保护作用。这两种涂层与基体之间形成了互扩散区(IDZ)和二次反应区(SRZ),IDZ和SRZ的厚度均随着循环氧化时间延长而增大;SRZ中析出的棒状与颗粒状的拓扑密堆相(TCP)含有W、Re、Mo等高熔点元素,其质量分数分别高达37.51%、14.22%和10.61%,TCP含量随着氧化时间而增多。活性元素Si、Hf对涂层中富Cr相和TGO的增长速率均有一定的抑制作用。

Ru/NiAlHf涂层在单晶高温合金界面的互扩散及循环氧化行为

采用电子束物理气相沉积(EB-PVD)的方法在第二代镍基单晶高温合金N5上先后沉积Ru层和NiAlHf涂层。利用X射线衍射(XRD)、扫描电镜(SEM)、能谱仪(EDS)等研究Ru/NiAlHf涂层与合金基体在1 100℃的界面上的互扩散行为及高温循环氧化性能。结果表明:在扩散初期,涂层与合金基体界面上处形成了不连续的Ru2AlTa相,该相有效抑制了高温合金基体中难熔元素的外扩散,而当扩散时间延长至100 h时,该相消失,同时合金基体中形成了少量拓扑密堆相(P-TCP),但未形成二次反应区(SRZ)。Ru/NiAlHf涂层在1 100℃循环氧化150h后氧化膜仍未出现显著剥落,表现出了良好的抗循环氧化性能。

Y-La添加对镍基单晶高温合金界面反应及循环氧化行为的影响

在第二代镍基单晶高温合金中复合添加Y-La,经定向凝固后得到5.26×10–4%(质量分数)Y+6.05×10–4%La和47.64×10–4%Y+69.09×10–4%La的两种Y-La含量合金铸件,研究Y-La对合金定向凝固过程中合金熔体与Al2O3基陶瓷间的界面反应行为以及合金在1100℃下循环氧化时抗氧化性能的影响。采用扫描电子显微镜、能谱仪和X射线衍射仪等研究合金熔体与陶瓷材料间的界面组织形貌及界面反应产物成分以及循环氧化后合金表面氧化物的组织形貌、元素组成和相关物相。结果表明:Y-La含量增加会促进合金熔体与陶瓷间的界面反应,使得界面反应层更厚,更复杂;反应产物主要是含Y、La的氧化物;Y-La添加明显提高了合金的抗氧化性能,减少合金表面氧化膜的剥落;但Y-La过量会恶化合金的抗氧化性能,加快合金的氧化增重速率;合金表面氧化膜剥落痕迹明显,孔洞较多且内氧化严重。