Modes of Grain Selection in Spiral Selector during Directional Solidification of Nickel-base Superalloys

The modes of grain selection in spiral selector were investigated by both a ProCAST simulation and experimental confirmation.The results show that the efficiency of grain selection in starter block is associated with the geometry shape.At the early stage of grain selection,the optimization of grain orientation is dominated by competitive grain growth,but the optimization of grain orientation in starter block is gradually dominated by geometry shape at the later stage of grain selection.Besides,the spiral part could also optimize the orientation of the selected single crystal when the initial angle is large enough,and the single crystal selection in spiral parts with different pitch lengths and initial angles is dominated by different modes.The simulation results agree well with experimental ones.     

高Cr铸造镍基高温合金K4648的母合金净度研究

对两炉冲击韧性存在明显差异的高Cr铸造镍基高温合金K4648进行了对比研究,通过分析两炉母合金的主量元素和气体含量,采用电子束纽扣锭(EB锭)实验观察合金内夹杂物和对母合金用原材料金属Cr的显微组织分析等方法研究了K4648母合金净度。结果表明:1#与2#炉批母合金主量元素无明显差别。1#母合金由于气体元素O含量高达(20.5±7.5)×10-6,远高于2#合金的6×10-6,造成其室温冲击韧性(aku)不及2#合金的一半,低于技术条件要求的19.6J/cm2。电子束纽扣锭(EB锭)实验可有效地将K4648中的夹杂物汇聚,经分析主要是富Y,Ce的氧化物和富Al氧化物。证明高Cr铸造镍基高温合金K4648中添加稀土元素Y,Ce可有效攫取合金中自由态的O和S,生成稳定的稀土氧化物或硫化物,起到净化合金的作用。K4648母合金原材料中金属Cr基体中固溶有15%(质量分数)的元素O,还分布有富Cr氧化物和Cr,Al,Si的复合氧化物。此外,还存在含N、贫O区域,该区域的维氏显微硬度可达8.2GPa,是Cr基体1.3GPa的6倍,证明N使金属Cr的硬度明显升高。     

热喷涂技术现场修复发电厂汽缸平面

通过分析发电厂汽缸平面的失效原因,研究了现场修复汽缸平面的技术方案、涂层材料和工艺流程。结果表明,配合适当工艺的热喷涂技术喷涂NiMo合金是现场修复汽缸平面的最佳方法。该技术已在发电厂获得了广泛应用,并取得了良好效果。     

比浊法检测镍基高温合金热腐蚀产物中硫酸根

研究硫酸钡比浊法检测镍基高温合金浸盐热腐蚀产物中硫酸根的化学分析方法．对测量波长、酸度、稳定剂、稳定时间对测量结果的影响进行测试．最佳实验条件：在50mL分析液内加入5mL盐酸、10mL丙三醇，稳定时间、测量波长分别为10min、470nm，该方法简便迅速，回收率为97.1％～101．9％，变异系数为1．33％～1．73％、适用于镍基高温合金浸盐热腐蚀产物中硫酸根的测定。     

Electron beam melting of Inconel 718: effects of processing and post-processing

ABSTRACT

This study reports the effect of process temperature on microstructure evolution of electron beam melted Inconel 718. Samples fabricated at 915°C had fine grain boundary δ (～200?nm) along with coarse intragranular δ spanning through the length of the grains. On the other hand, samples fabricated at 990°C, only had grain boundary δ along with secondary carbides. During hot isostatic pressing, the distribution of carbides governs the grain growth vs. lack of it. The samples fabricated at 990°C having grain boundary carbides had no grain growth owing to the pinning effect of carbides. In contrast, the sample processed at 915°C had significant grain growth owing to dissolution of grain boundary δ phase and absence of grain boundary carbides.     

High temperature characteristics of Ir–Ta coated and aluminized Ni-base single crystal superalloys

High temperature oxidation and hot corrosion properties of Ir–Ta coated and aluminized Ni-base superalloys are presented. An Ir–Ta binary alloy, proposed as a novel metallic bond coat material, was coated on a Ni-base single crystal superalloy TMS-75 using electron beam physical vapor deposition, followed by a conventional low activity Al pack cementation process. Cyclic oxidation tests and hot corrosion tests revealed that these Ir–Ta coated and aluminized specimens showed reasonably good oxidation and hot corrosion resistance. In addition, it was found that the formation of TCP phases is suppressed by the presence of the Ir–Ta enriched layer. These results indicated that the Ir–Ta alloy system is promising as a new metallic bond coat material for high temperature structural materials.     

Substrate Effect on the High Temperature Oxidation Behavior of a Pt-modified Aluminide Coating. Part II: Long-term Cyclic-oxidation Tests at 1,050 °C

This second part of a two-part study is devoted to the effect of the substrate on the long-term, cyclic-oxidation behavior at 1,050 °C of RT22 industrial coating deposited on three Ni-base superalloys (CMSX-4, SCB, and IN792). Cyclic-oxidation tests at 1,050 °C were performed for up to 58 cycles of 300 h (i.e., 17,400 h of heating at 1,050 °C). For such test conditions, interdiffusion between the coating and its substrate plays a larger role in the damage process of the system than during isothermal tests at 900, 1,050, and 1,150 °C for 100 h and cyclic-oxidation tests at 900 °C which were reported in part I [N. Vialas and D. Monceau, Oxidation of Metals 66, 155 (2006)]. The results reported in the present paper show that interdiffusion has an important effect on long-term, cyclic-oxidation resistance, so that clear differences can be observed between different superalloys protected with the same aluminide coating. Net-mass-change (NMC) curves show the better cyclic-oxidation behavior of the RT22/IN792 system whereas uncoated CMSX-4 has the best cyclic-oxidation resistance among the three superalloys studied. The importance of the interactions between the superalloy substrate and its coating is then demonstrated. The effect of the substrate on cyclic-oxidation behavior is related to the extent of oxide scale spalling and to the evolution of microstructural features of the coatings tested. SEM examinations of coating surfaces and cross sections show that spalling on RT22/CMSX-4 and RT22/SCB was favored by the presence of deep voids localized at the coating/oxide interface. Some of these voids can act as nucleation sites for scale spallation. The formation of such interfacial voids was always observed when the β to γ′ transformation leads to the formation of a two-phase β/γ′ layer in contact with the alumina scale. On the contrary, no voids were observed in RT22/IN792, since this β to γ′ transformation occurs gradually by an inward transformation of β leading to the formation of a continuous layer of γ′ phase, parallel to the metal/scale interface.     

奥氏体基体灰铸铁与镍基合金复合玻璃模具材料的研究

用石墨粉保护电炉加热的方法制备奥氏体基体灰铸铁与镍基合金复合玻璃模具材料，用光镜、显微硬度计、扫描电子显微镜及能谱分析仪和万能实验机对复合层及界面的显微组织、显微硬度、成分分布和剪切强度进行了相应的观察和测试。结果表明：奥氏体基体灰铸铁由于碳含量低发生少量的马氏体、贝氏体转变；随着温度的升高，元素的扩散作用加剧，过渡区变宽，剪切强度有增大的趋势，同时，基体对复合层的稀释作用也明显，使复合层的性能下降。     

镍基高温合金GH4049高温疲劳小裂纹扩展规律

对镍基高温合金GH4049在相同载荷、不同温度下疲劳小裂纹扩展规律进行了试验，利用复型技术和光学显微镜观测了裂纹尺寸演化全过程，发现小裂纹扩展速率的趋势是先快后慢，且温度升高，扩展速率反而下降。这与小裂纹的闭合效应有关，在700％小裂纹的氧化诱发闭合效应比650％时明显。     

细观非均质性对镍基单晶双相合金塑性行为的影响

建立了考虑背应力演化和损伤演化的晶体塑性模型，利用所建立的晶体塑性模型研究了应变速率对镍基单晶合金基体相、强化相的影响。结果表明，镍基单晶基体相和强化相均表现出明显的率相关性。单晶双相合金的细观非均质性导致非均匀的微观应力和微观塑性滑移。塑性滑移变形首先发源于基体相。微观应力和塑性滑移的非均匀性可能是材料微观损伤积累和孔洞形核的根源。