TEM studies of oxidized NiAl and Ni3Al cross sections

Doychak, J.; Rühle, M.

doi:10.1007/bf00666466

Cited by 167 publications

(59 citation statements)

References 15 publications

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“…This behavior is in agreement with previously reported results [ 8,11]. The initial tensile stress is attributed to the transformation of the first-formed alumina to the more stable alpha form, since this process involves a volume reduction [20]. After the phase transformation was complete, the stress became near zero.…”

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confidence: 93%

Growth Strains and Stress Relaxation in Alumina Scales during High Temperature Oxidation

Hou

Paulikas

Veal

2004

MSF

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Abstract.A novel X-ray technique was used, exploiting synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory, to investigate the growth stresses in α-Al 2 O 3 . In-situ measurements of Debye-Scherrer diffraction patterns from the scale were recorded during oxidation and cooling, and the elliptical distortion of the diffraction rings was analyzed to yield the in-plane strain. Fe28Al, and Ni-50Al (at. %) were studied. Data were acquired in air at temperatures between 950-1100 o C and during cool down. In all cases, the steady stage growth strain was relatively low (<0.1%) and was either tensile or compressive depending on the alloy. A higher tensile strain often existed during the initial oxidation period when transition alumina was present. Thermal stresses imposed on NiAl by reducing the sample temperature to 950 o C for a period of time showed noticeable stress relaxation by creep. Different degrees of relaxation were also found during cooling depending on alloy composition and scale microstructure. On all Fe-based alloys, the first formed α-Al 2 O 3 was highly textured with the degree of texture decreasing with further oxidation. The relationships between stress development, scale wrinkling, oxide phase changes, and the effect of reactive element addition on growth stresses are discussed. Results are compared with other reports of growth stresses in Al 2 O 3 scales.

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confidence: 93%

Growth Strains and Stress Relaxation in Alumina Scales during High Temperature Oxidation

Hou

Paulikas

Veal

2004

MSF

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“…Unlike Ni 3 Al, where NiO and Ni-Al spinels were often found at the outer scale surface [7][8][9] alloy, without any Cr addition, has also been found by EDS/SEM and X-ray diffraction [16,19] Before oxidation, a room temperature, or native, oxide thin film exists on the alloy surface, as observed by AES depth profile, similar to those shown in Fig. 1.…”

Section: Discussionsupporting

confidence: 65%

Al₂O₃scale development on iron aluminides

2006

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“…The oxidation behavior ofNiAl has been studied extensively [10][11][12][13][14][15][16][17][18]. The firstformed oxide is eor y-Ah03 that grows mainly by cation outward transport [11,15].…”

mentioning

confidence: 99%

“…Because of this phase transformation, the oxidation kinetics show two parabolic stages separated by a gradual transition. At 1000°C, the rate constant for the initial stage is about 10-12 g2/cm4s, and it is more than two orders of magnitude faster than the later steady state [12]. Interfacial voids that are several times larger in diameter than the oxide grain sizes are often observed on the alloy surface [10,[18][19][20].…”

mentioning

confidence: 99%

Interfacial Segregation, Pore Formation, and Scale Adhesion on NiAl Alloys

2005

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Ni-40 and 50at%AI alloys were oxidized at 1000°C for various times in oxygen. Auger electron microscopy was used to study the interface chemistry after scale spallation in ultra high vacuum. The interfacial failure stresses were determined using a tensile pull tester and related to the interface chemistry, pore area and density. Results showed that sulfur started to segregate to areas ofthe Ah03INi40AI interface where the scale was in contact with the alloy after a complete layer of a-Ah03 developed there; the concentration then gradually increased to a steady level of~2 at%. However, sulfur did not segregate to similar areas of the Ah03INi50AI interface even after extended oxidation when it was amply present on interfacial void faces. This behavior demonstrated a strong dependence of interface segregation on NiAI alloy composition. Interfacial failure stress was found to decrease with increasing sulfur content between voids and with higher interface porosity. The level of porosity was strongly related to the sulfur content in the alloy. When Ni40AI was doped with excess sulfur, the segregation behavior did not change, but the interfacial pore density increased significantly. The detrimental effect of sulfur on scale adhesion is two-fold: to weaken the interface and to enhance interfacial pore formation.

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TEM studies of oxidized NiAl and Ni3Al cross sections

Cited by 167 publications

References 15 publications

Growth Strains and Stress Relaxation in Alumina Scales during High Temperature Oxidation

Growth Strains and Stress Relaxation in Alumina Scales during High Temperature Oxidation

Al₂O₃scale development on iron aluminides

Interfacial Segregation, Pore Formation, and Scale Adhesion on NiAl Alloys

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TEM studies of oxidized NiAl and Ni3Al cross sections

Cited by 167 publications

References 15 publications

Growth Strains and Stress Relaxation in Alumina Scales during High Temperature Oxidation

Growth Strains and Stress Relaxation in Alumina Scales during High Temperature Oxidation

Al2O3scale development on iron aluminides

Interfacial Segregation, Pore Formation, and Scale Adhesion on NiAl Alloys

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Al₂O₃scale development on iron aluminides