Tadaaki Amano

The effects of yttrium addition on high-temperature oxidation of heat-resistant alloy with sulfur

Abstract The effects of yttrium (10, 300 and 3700 ppmY) addition on high-temperature oxidation of Fe–20Cr–4Al alloy with sulfur (185 ppmS) were studied in air for 1800 ks at 1273, 1373 and 1473 K by mass-change measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Oxide scales on all of the alloys showed good adherence after oxidation at 1273 K. On the other hand, oxide scales on the 185 ppmS and 10 ppmY alloys spalled from the entire surface, and those on other alloys did not spall after oxidation at 1373 and 1473 K. Mass gains of the alloys with yttrium addition tended to increase with increasing content of yttrium. Oxide scales on the 185 ppmS alloy showed a convoluted morphology, however, surface morphologies of those on the other alloys with yttrium changed to planar with increasing yttrium content after oxidation at 1273 K. Oxide scales on all of the alloys were almost planar after oxidation at 1373 and 1473 K. Behavior of sulfur and yttrium will be presented after oxidation.

Cyclic-Oxidation Behavior of Fe–20Cr–4Al Alloys with Small Amounts of Sulfur at High Temperatures

The cyclic-oxidation behavior of Fe–20Cr–4Al alloys with 3, 35, 53, 104, and 171 ppm sulfur was studied in oxygen at 1273, 1373, 1473, 1573, and 1673 K by mass-change measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron-probe microanalysis (EPMA). The cyclic oxidation consisted of an 18.0 ksec exposure that was repeated up to five times. Amounts of spalled oxides of the alloys with 35 and 53 ppm sulfur increased after one and two oxidation cycles, and then decreased after three or more oxidation cycles at 1473 and 1573 K. On the other hand, spalling of oxide scales on the alloys with 3 and 171 ppm sulfur was scarcely recognized after all cycles used in this study. SEM observations of both sides of the spalled oxides indicated that spallation was related to the morphology of the surface oxides and to the morphology and volume of cavities at the oxide–alloy interface.

The morphology of alumina scales formed on Fe-20Cr-4Al-S alloys with reactive element (Y, Hf) additions at 1273 K

Abstract The morphology of alumina scales formed on Fe–20Cr–4Al–S (185 ppm) alloys with reactive elements (10, 300, 800, and 3700 ppmY, 500, 900, 1900, and 4300 ppmHf) was studied in oxidizing atmospheres at 1273 K for 18, 1800 and 3600 ks by mass gain measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). No spalling of the oxide scales was observed on any of the alloys after any of the oxidation times. Mass gain decreased for alloys with small additions of reactive elements, and then increased with increasing reactive element content. Oxide scales on the 185 ppmS, the 500 and 900 ppmHf alloys showed a wavy morphology. On the other hand, oxide scales on the other alloys with reactive elements changed from small wavy to planar morphologies with increasing reactive elements after any of the oxidation times studied. Oxide scales formed on all of the alloys were recognized as mainly _-Al2O3. After oxidation for 3600 ks, Y3Al5O12 particles were observed for the 800 and the 3700 ppmY alloys, and HfO2 particles were also detected for the 1900 and the 4300 ppmHf alloys.

Boron-carbon atomic ratio dependence on the hardness and oxidation resistance of solid solutions of perovskite-type borocarbide YRh3BxC1-x (0 ≤ x ≤ 1)

Solid solutions of the quaternary borocarbide system YRh3BxC1-x have been synthesized and studied from the viewpoints of their microhardness and oxidation resistance. Perovskite-type YRh3B and YRh3C form a continuous solid solution in the range of 0?x?1 with a cubic structure (space group: Pm3m, Z=1). The microhardness of YRh3BxC1-x increases with increasing boron content. The oxidation onset temperature also increases with boron content. Thus, it is indicated that the chemical stability of solid-solution YRh3BxC1-x is strongly dependent on the boron content.

Oxide adherence of Fe-20Cr-4Al alloys with small amounts of sulfur and reactive elements (Y,Hf)

Abstract Oxide adherence of Fe–20Cr–4Al alloys with small amounts of sulfur, yttrium and hafnium was studied in air for 360 ks at 1,373, 1,473 and 1,573K by mass change measurements, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. After oxidation at 1,373K, spalling of oxide scales on 7ppmS, 53ppmS and 1,300ppmS alloys was recognized. However, spalling of oxide scales on the other alloys was not observed. After oxidation at 1,573K, spalling of the oxide scales on the alloys with sulfur increased roughly with increasing contents of sulfur, and spalling of oxide scales on the alloys containing yttrium was scarcely recognized, however, oxide scales on all of the alloys containing hafnium spalled at the entire surface. Oxide adherence on the alloys may relate to morphologies of oxide scales and oxide–alloy interface, size and distribution of chromium sulfide, Y3Al5O12 and HfO2 particles at the oxide–alloy interface and temperature of oxidation.

Spalling of the surface oxide formed on Ni-(20,40,60,80)Cr alloys with small additions of Ce and Si

Abstract The oxidation behavior of Ni-(20,40,60,80)Cr alloys and the alloys with small additions of Ce and Si was studied for 14.4 ks at 1523 K in O 2 by mass-change measurements, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray microanalysis.

Hardness and oxidation resistance of perovskite-type borocarbide system YRh3BxC1−x (0≦x≦1)

Abstract Quaternary borocarbide system YRh 3 B x C 1− x phase have been synthesized by arc melting method and studied for their microhardness and oxidation resistance. Perovskite-type YRh 3 B and YRh 3 C form a continuous solid–solution in the range of 0≦ x ≦l with a cubic structure (space group: Pm 3 m , Z =1). The microhardness of YRh 3 B x C 1− x increases with increasing boron content. Thermogravimetric analysis indicates that the oxidation onset temperature also increases with boron content. Thus, it is indicated that the chemical stability of the perovskite-type borocarbide solid–solution YRh 3 B x C 1− x is strongly dependent on the boron content.

The cyclic oxidation of Ni-20Cr alloys with small additions of cerium and silicon

The cyclic oxidation behaviour of Ni-20Cr, Ni-20Cr-1Si, Ni-20Cr-3Si, Ni-20Cr-0.3Ce, Ni-20Cr-1Si-0.3Ce and Ni-20Cr-3Si-0.3Ce alloys was studied in O 2 . Cyclic oxidation testing consisted of a 3.6 ks exposure at 1000 and 1100 o C followed by a minimum cooling period of 1.2 ks, during which the specimen temperature reached approximately 40 o C. This oxidation-cooling cycle was repeated up to five times. At 1000 o C, mass gains of the alloys increascd in the order of Ni-20Cr-1Si-0.3Ce<Ni-20Cr-0.3Ce <Ni-20Cr-3Si<Ni-20Cr-3Si-0.3Ce<Ni-20Cr-1Si<Ni-20Cr alloys, and surface oxides of Ni-20Cr, Ni-20Cr-1Si and Ni-20Cr-3Si alloys spalled at the oxide/alloy interface

Adherence of alumina scale formed on Fe–20Cr–4Al alloys with noble metals (Pd, Pt)

Abstract Adherence of oxide scale formed on Fe–20Cr–4Al (standard: 4 ppmS), Fe–20Cr–4Al (FZ: <1 ppmS) purified by floating zone melting, and Fe–20Cr–4Al–(0.05, 0.1, 0.3, 0.5)–Pd(Pt) alloys was studied in oxygen for 18 ks at 1373–1673 K, by mass gain measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Spalling of oxide scale on the standard alloy occurred along the alloy grain boundaries after oxidation at 1373 K, and was found to spall over the entire surface after oxidation at 1473 and 1573 K. However, the standard alloy showed good oxide adherence after oxidation at 1673 K. The other alloys showed good oxide adherence after oxidation at any temperature. Mass gain of the FZ and noble metal-containing alloys increased with increasing temperature of oxidation, and showed almost the same values at each temperature. Oxide scale on the standard alloy showed wavy morphology after oxidation at 1373 and 1473 K, and changed to planar morphology after oxidation at 1573 and 1673 K. On the other hand, oxide scale on the other alloys showed almost planar morphology after oxidation at any temperature. Oxide scale formed on all the alloys was only found to be α-Al2O3 after oxidation at any temperature.

High-temperature oxidation of FeCrAl(Y, Pt) alloys in oxygen–water vapour

Abstract High-temperature oxidation behaviour of FeCrAl(Y, Pt) alloys was studied in oxygen and oxygen – water vapour (47 vol%) for 18 ks at 1473, 1573 and 1673 K, by mass gain measurements, the amount of spalled oxide, X-ray diffraction, scanning electron microscopy and field emission-transmission electron microscopy – energy dispersive spectroscopy. After oxidation at 1473K for 18 ks in oxygen, the mass gain of the FeCrAl alloy with appropriate addition of both yttrium and platinum was the smallest value, and alumina – alloy interface of the alloy showed good coherency by TEM. After oxidation at 1673K in oxygen – water vapour (47 vol%) for 18 ks, the amount of spalled oxide of FeCrAl0.5Pt alloy was zero. This result is thought to relate to the formation of concentrated platinum layer at the oxide – alloy interface. Spalling of oxide scale on FeCrAl and FeCrAl0.1Y alloys was observed, however, oxide scale on FeCrAl0.5Y alloy showed good adherence during five cycles (one cycle=18 ks) in oxygen – water vapour (47 vol%) at 1573 K.