EFFECT OF MICROSTRUCTURE CHANGE ON OXIDE FORMATION OF SPUTTERED Ni-3Cr-10Al NANOCRYSTALLINE COATING

The microstructure change of sputtered Ni-3Cr-10Al nanocrystalline coating during oxidation in air at 900°C was observed and its eNct on oxide formation on the sputtered coating was studied. Twe results indicated that Ni3Al was segmpated during oxidation, on which Nio could be easily formcd. NiO could react with the trunsient γ-Al2O3 to form NiAl2O4 through solid reaction, whtch can be found on the oxide scale afer 200h oxidation. Thewtre, the oxide scale formed on sputtered Ni-3Cr10Al coating was not composed of a unltary layer of Al2 O3. Thc Al2O3 and NiAl2 O4 complex oxide scale bonded properly with substrate and showed gpod adhesion and good oxidation resistance.

Oxide formation on sputtered Ni-3Cr-10Al nanocrystalline coating

The oxide formation on the sputtered Ni 3Cr 10Al nanocrystalline coating at 900 ℃ and 1 000 ℃ in air has been studied. The results indicated that an oxide scale composed of NiAl 2O 4 and Al 2O 3 was formed on the sputtered Ni 3Cr 10Al nanocrystalline coating whereas a unitary Al 2O 3 scale was not formed even when the Al content was high in the sputtered coating. The formation of NiAl 2O 4 was directly related to the precipitation of Ni 3Al in the coating during oxidation process. It was suggested that the precipitation of Ni 3Al contributed to the formation of NiO and therefore NiO could react with Al 2O 3 and form NiAl 2O 4. With increasing oxidation temperature, the effect of Ni 3Al precipitation on the formation of NiAl 2O 4 decreased.

Ti-10V-2Cr-3Al钛合金的高温压缩变形行为及本构关系

在应变速率0.1~0.001 s^(-1)、变形温度730~880℃下对Ti-10V-2Cr-3Al钛合金进行热压缩试验,研究了该合金的热变形行为和显微组织;利用唯象Arrhenius^(-1)方程中指数方程及双曲正弦方程描述流动应力与变形温度、应变速率之间的关系,构建了应变补偿修正的本构方程并进行了验证。结果表明:在试验条件下合金的真应力随着应变速率的增加或变形温度的降低而增大;当应变速率为0.01 s^(-1)时,在α+β相区(730,790℃)压缩后试验合金中出现球状和短棒状α相,软化机制为动态球化和动态再结晶,在β相区(820,880℃)压缩后出现再结晶β晶粒,软化机制为动态再结晶;当应变速率在0.1~0.05 s^(-1)和0.01~0.001 s^(-1)范围时,可分别使用修正后的指数方程和双曲正弦方程来描述试验合金的流变行为,流动应力预测值与试验值的平均相对误差为5.36%,这说明修正后的方程具有良好的预测能力。

预氧化温度对Ni-20Cr-5Al-0.2Y2O3合金抗高温循环氧化性能的影响

通过粉末冶金方法制备了Ni-20Cr-5Al和Ni-20Cr-5Al-0.2Y_2O_3(质量分数/%,下同)合金,将Ni-20Cr-5Al-0.2Y_2O_3合金在不同温度(500~1 100℃)进行预氧化处理,然后将未预氧化及预氧化合金在1 150℃下循环氧化15h,研究了Y_2O_3的添加和不同预氧化温度对合金抗高温循环氧化性能的影响。结果表明:添加0.2%Y_2O_3后提高了Ni-20Cr-5Al合金的抗高温循环氧化性能;预氧化可以有效提高Ni-20Cr-5Al-0.2Y_2O_3合金的抗高温循环氧化性能,其中预氧化温度为700℃的合金有最优的抗高温循环氧化性能,其原因是经过预氧化处理的合金表面形成了致密的保护性氧化膜,阻止了氧化的进一步进行。

Y_2O_3含量对Ni-5Al与Ni-10Al合金在1100℃下抗氧化性能的影响

采用粉末冶金技术制备了不同Y_2O_3含量的Ni-5Al和Ni-10Al合金,并在1100℃下对合金进行100 h循环氧化实验。研究了Y_2O_3含量对Ni-Al合金高温抗氧性能的影响。结果表明:添加Y_2O_3会促进Ni-5Al合金中NiO的生成,随着Y_2O_3含量的增加,NiO的生长速度加快,晶粒变大,使Ni-5Al合金高温抗氧化性能随Y_2O_3含量的增加逐渐降低。在Ni-10A合金中,Y_2O_3的添加会促进Al2O3的择优生长,增强氧化膜与基体的粘附性,提高合金的高温抗氧化性能,最优添加值为0.6wt%。Ni-10Al-x Y_2O_3合金的高温抗氧化性能明显优于Ni-5Al-x Y_2O_3(wt%,x分别为0,0.2,0.6,1.0)合金的。

Oxidation Behaviour of Sputtered Ni-3Cr-20Al Alloy

The oxidation behavior of sputtered Ni-3Cr-20Al coating at 900℃ in air was investigated. A dense Al2O3 layer was formed on the sputtered Ni-3Cr-20AI coating after 200 h oxidation. However, owing to the segregation of Ni3Al during oxidation process at high temperature, the spinel NiAI2O4 was also formed in the Al2O3 layer. It was found that the formation of NiAI204 had no detrimental effect on the oxidation resistance of the sputtered N?3O-20AI coating due to the excellent adhesion shown by the Al2O3 and NiAl2O4complex oxide scale.

Al对Fe-20Cr-35Ni-0.6Nb合金显微组织和抗氧化性的影响

采用增量法研究了不同Al含量(0.5%、1.5%、2.5%,质量分数)的Fe-20Cr-35Ni-0.6Nb含Nb合金在1000℃空气条件下的抗氧化。采用SEM、EDS、TEM、拉曼光谱等手段研究了合金的显微组织和氧化膜特性。结果表明,3种含Nb合金组织为单相奥氏体,基体中存在少量弥散分布的NbC沉淀相,氧化前后沉淀相含量和晶粒大小保持不变。添加0.5%和1.5%的Al后,含Nb合金的表面形成多层结构的氧化膜,最外层和第三层为Cr_(2)O_(3),次表层主要为NiCr_(2)O_(4)、NiFe_(2)O_(4)和Fe_(2)O_(3),最内层为Al_(2)O_(3)内氧化层。基体中的NbC析出相和氧化膜中少量Nb的氧化物(Nb_(2)O_(5))加剧了氧化膜的疏松。当Al含量增加到2.5%时,含Nb合金表面形成连续致密的Al_(2)O_(3)氧化膜,降低了Fe-20Cr-35Ni-0.6Nb合金的氧化速率,提高了抗氧化性。

新型含铝Fe-Cr合金的热变形行为及热加工图

采用Gleeble-3500热模拟试验机对Fe-18Ni-12Cr-3Al合金进行压缩试验,其变形温度为925~1175℃、应变速率为0.01~10 s^(-1)。分析了合金真应力-真应变曲线,建立了本构方程及热加工图,并结合θ-σ曲线上的拐点,采用拐点法研究其动态再结晶的临界条件。结果表明,Fe-18Ni-12Cr-3Al合金应力随着应变速率增加和变形温度降低而升高,发生动态再结晶的临界应力和峰值应力之间具有相关性,即σ_(c)=0.95σ_(p)。依据热本构方程和热加工图,热激活能为376.1 kJ/mol,应变为0.1时的最佳热加工区域是变形温度为1110~1160℃,应变速率为0.01~1 s^(-1)。