Ks In Air Research Articles

The influence of high-temperature oxidation on the phase distribution of metal substrate in duplex stainless steel

Duplex stainless steels (DSSs), which consist of ferrite and austenite phases, are widely used owing to their high strength and good corrosion resistance. However, the oxidation behavior of DSSs is extremely complicated because they have dual phases. In this study, changes in the scale and the metal substrate during oxidation were investigated. UNS S32101 (Fe-21.5%Cr–5%Mn–1.5%Ni–0.3%Mo–0.22%N), which is a typical type of DSS, was annealed at 1473 K for up to 36 ks in air. The microstructure of UNS S32101 consisted of austenite/ferrite phases, the ratio of which was 50:50 at room temperature. After oxidation, Cr, Mn-oxide formed predominantly. The metal substrate beneath the scale changed mostly to ferrite. In the same region, depletion of Mn and N concentrations resulted. The decrease in Mn was due to the formation of Cr, Mn-oxide. In addition, it was revealed that N content of the metal substrate decreased due to the formation of N2 gas along with the depletion of Mn. It was assumed that the decrease in Mn and N, which are austenite-stabilized elements, led to an increase in ferrite in the depletion area of Mn and N. From this result, it was expected that the compositional changes in the Mn/N depletion area were caused by the oxidation of steel.

Effect of Microshot Peening on Fatigue Strength of Austenite Stainless Steel

The effects of the peening conditions on the surface characteristics and fatigue strength of stainless steel were investigated by microshot peening (MSP). In recent years, MSP technology has attracted attention. The use of MSP technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. However, the effect of MSP technology on stainless steel has not been much studied. In the present study, an air-type machine was used. The media used was high-carbon cast steel (490 HV) and Fe-Cr-B alloy (1130 HV), with an average diameter of 0.1 mm. The peening time was in the range of 0 - 100 s. Four types of stainless steels, SUS304, SUS304L, SUS316, and SUS316L, were tested. The workpieces were annealed at 1100 K for 1.2 ks in air. In the measurement of fatigue strength, the workpieces were machined in hour-glass shape. As the results, surface roughness of the workpieces treated by MSP was small. Work hardening was evident to the depth of approximately 0.2 mm from the surface. This depth was about twice the diameter of shot media. However, the effect of the peening time on the hardness distribution was not large. The compressive residual stress was added in the surface vicinity. It is assumed that the fatigue limit had increased because the work hardened layer was formed near the workpiece surface.

Liquid-Phase Oxidation Joining of Yttria-Stabilized Zirconia via Al/Fe-Cr Alloy/Al Interlayers

Liquid-phase oxidation (LPO) joining technique was employed to join yttria-stabilized zirconia (YSZ) blocks using Al/Fe-Cr alloy /Al interlayer for development of a gas sealing technique for solid oxide fuel cells (SOFCs). The YSZ blocks were joined at 1073 to 1473 K for 3.6 to 28.8 ks in vacuum (< 0.2 Pa) with a stress of 80 MPa and annealed at 973 K for 3.6 ks in air. The average four-point bend strength and Weibull modulus of LPO-joined YSZ specimen increased with increasing joining time at 1273 K. The specimen joined at 1273 K for 28.8 ks has a four-point bend strength of 135 MPa, which was about four times greater than that obtained by brazing technique using Ag solder, and comparable to unbonded monolithic YSZ. Polycrystalline alumina layer, which is expected to act as an insulating and protective layer, was formed between YSZ and Fe-Cr alloy after the LPO joining.

Calcium phosphates formation on CaTiO3 coated titanium

In this study, performance of calcium phosphate formation of CaTiO3 coating film on Ti in Hanks' balanced saline solution (HBSS) was investigated. CaTiO3 thin films with a thickness of 50 nm were deposited on Ti using radiofrequency (RF) magnetron sputtering. The temperature of Ti substrate was adjusted to room temperature (RT) and 873 K. Thereafter, the specimens deposited at RT were annealed at 873 K in air for 7.2 ks. The films were characterized by grazing incident angle X-ray diffractometry (GI-XRD) and X-ray photoelectron spectroscopy (XPS). After immersion in HBSS for 60 d, on CaTiO3 coated Ti, the formation of hydroxyapatite (HAP) was observed. Furthermore, HAP layer formed was thicker on the specimen on which CaTiO3 film was deposited at RT and annealed than that prepared at 873 K. The major difference between both specimens was the chemical properties of the outermost surface. In summary, CaTiO3 thin film deposited at RT and followed by annealing at 873 K for 7.2 ks in air enhances calcium phosphate formation ability on Ti.

Oxidation behavior of a γ-TiAl-based alloy implanted by silicon and/or carbon

A study has been made of isothermal oxidation behavior of a γ-TiAl-based alloy, Ti–48Al–1.3Fe–1.1V–0.3B (at.%), implanted with silicon and/or carbon ions at 1173K, C+Si double implantation and following annealing at 1123K for 10.8ks. The isothermal oxidation was tested at 1173K for 349.2ks in air. Si or C implantation was carried out with a dose of 3.0×1021ions/m2 and at the acceleration voltage of 50 and 70kV. As-implanted specimen and the specimen oxidized under specified conditions were characterized by Auger electron spectroscopy (AES), X-ray diffractometry (XRD) and scanning electron microscopy (SEM).High-temperature Si implantation at 1173K shows better oxidation resistance than that implanted at room temperature (RT) for the long-term oxidation. The C introduction by C+Si double implantation weakened the beneficial effect of Si, and the following annealing improved its oxidation resistance. Si doping in the TiAl alloy could facility the Al2O3 formation in the early stage of the oxidation through the enhancement of the Al activity, and C doping is harmful because of a porous oxide scale. From this study, it is indicated that high-temperature implantation at 1173K is effective to thicken the Si-modified layer and thus, a strong and long-term Si modification effect. No cooperation effect of C and Si can be observed for C+Si double implantation to intensify the Si beneficial effect.

Ａｌの溶融塩電析による金属Ｎｂの表面改質とその耐高温酸化性

The surface improvement of Nb to improve the high temperature oxidation resistance was carried out by Al electrodeposition using the molten salt as an electrolyte. Electrolysis of Al was conducted using potentiostatic polarization method at constant potentials in an equimolar NaCl-KCl melt containing 1∼5 mol%AlF3 at 1023K. The mass of electrodeposited Al increased with a decrease in polarization potential. Deposits formed at -1.3∼-1.6V (vs. Ag/Ag+ (0.1)) consisted of hemispherical Al phase and lamellar Nb-Al alloy phase. The alloy phase consisted of NbAl3. Niobium covered by the Nb aluminide was more resistant than bare niobium to high temperature oxidation at 1273K for 10.8ks in air.

生体用Ti-XNb-10Ta-5Zr合金のミクロ組織，引張特性および弾性率に及ぼすNb添加量の影響

Effect of Nb content on microstructure, tensile properties and elastic modulus of Ti-XNb-10Ta-5Zr alloys made by a sinter-forged method for biomedical applications was investigated. Ti-30Nb-10Ta-5Zr, which is the simplified compositional alloy of Ti-29Nb-13Ta-4.6Zr developed for biomedical applications, has been selected as the basic alloy composition and, Nb contents of the alloy were varied from 0 through 40 mass%.Blended elemental powder metallurgy method was applied to fabricate these alloys. The alloying elements powders were mixed and pressed to form green products by a cold isostatic pressing (CIP) machine. Green products were then sintered at 1573 K for 57.3 ks in a vacuum of about 1.33×10−3 Pa. Subsequently, they were forged and swaged at 1223 K in air. Finally, heat treatment at 1123 K for 1.8 ks in air to remove residual strain was done on the swaged bar. Tensile tests and elastic modulus measurements and mocrostructural observations on different Nb content were carried out.The microstructure of the alloy containing 0 mass%Nb shows single α phase. Other phases such as α″ phase, ω phase and β phase become to be recognized with increasing Nb composition of Ti-XNb-10Ta-5Zr alloys. Microstructures of the alloys containing over 30 mass%Nb show single β phase.Elastic moduli of Ti-XNb-10Ta-5Zr alloys decrease with increasing Nb contents. However, 15Nb, 20Nb and 25Nb alloys, whose microstructures contain ω phase, show a tendency of the increase of elastic moduli. These tendencies of elastic moduli are the same with general binary titanium alloy systems.The alloy containing 25 mass%Nb, whose microstructure have ω phase, shows the largest elongation. Tensile properties of the alloys containing over 30 mass%Nb, which have same microstructures, change a lot. These phenomena are caused by the change of deformation mechanism of β phase.

Microstructure and Thermoelectric Properties of NaxCo2O4 Synthesized by Spark Plasma Sintering.

The synthesis of the NaxCo2O4 thermoelectric oxide was tried by mechanical grinding (MG) and spark plasma sintering (SPS). The effects of the synthesis process on its microstructure and thermoelectric properties were investigated. The sample prepared by MG for 72 ks and SPS under 40 MPa at 773 K for 0.9 ks in air was composed of the Co3O4 and CoO phases, and NaxCo2O4 phase formation did not occur. In the case that the MG powder was calcined at 1183 K for 3.6ks in air and then subjected to SPS at 1073 K in vacuum, the sample was mostly composed of the NaxCo2O4 phase with several Co oxides. These Co oxides remained present even after subsequent annealing at 1083 K for 72 ks in air. On the other hand, in the case of SPS at 773 K for 0.9 ks in air and subsequent annealing, the sample was composed of the NaxCo2O4 phase without any other impurity phases. Besides that, a significant fine microstructure as compared to that of the pressurelessly sintered sample, could be obtained for this sample. However, the thermal conductivity of the sample was higher than that of the sample prepared by the conventional solid state reaction, i.e., calcination and subsequent pressureless sintering. This is considered to be associated with a degree of the crystallographic orientation of the compacts.

Improvement in the Oxidation Resistance of an Al-Deposited Fe–Cr–Al Foil by Preoxidation

The oxidation kinetics of conventional Fe–20Cr–5Al (in mass %) foil, Al-deposited foil and Al-deposited and preoxidized foil was studied at 1373 K in air. All the foils were 50-μm thick and contained minor additions of rare-earth elements. The oxide scales were observed with SEM and TEM combined with EDS and were characterized with X-ray diffractometry and electron diffraction. The deposition of Al onto the foil from the vapor phase improves oxidation resistance. The details regarding this matter were reported elsewhere. The combination of the Al deposition and the subsequent preoxidation at 1173 K for 90 ks in air further increases the oxidation resistance, i.e., the smallest parabolic rate constant among the three kinds of foils, and excellent scale adherence. Preoxidation enhances the growth of θ-Al2O3, which transforms to α-Al2O3 during subsequent oxidation. However, such α-Al2O3 grains are much larger than those formed on the conventional foil of similar chemical composition. Small closed voids and small spinel-type, oxide particles appear in α-Al2O3 grains with the progress of oxidation. The former is explained in terms of the volume decrease accompanying the phase transformation and the latter by the low solubility of Fe in α-Al2O3.

Oxidation behavior of TiAl protected by Al and Nb combined ion implantation at high temperature

The combined ion implantation of Nb at 1173 K and Al at 973 K on a γ-TiAl based alloy Ti–48Al–1.3Fe–1.1V–0.3B (at.%) was conducted with a dose of 3.0×10 17 ions/cm 2 and at an accelerating voltage of 50 kV for each element with different sequences. The implanted layer was contaminated by C during the Nb implantation at 1173 K. The isothermal oxidation behavior of the above-treated alloys was investigated at 1173 K for 349.2 ks in air using a thermobalance. Auger electron spectroscopy (AES), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were employed to characterize the modified layer and oxide scale. The Al + Nb implanted alloy shows excellent long-term oxidation resistance due to the formation of a continuous and compact Al 2O 3 oxide scale. The co-existence of Nb and C in conjunction with the Al enrichment in the modified layer could inhibit the inward diffusion of O and prolong the beneficial effect of Nb and thus lead to the formation of the above protective scale. To the contrary, the oxidation rate of the Nb + Al implanted alloy remained very low in the first about 100 ks exposure and then accelerated. It is concluded that the C beneficial effect derived from the Nb and C layer formed during the 1173 K Nb implantation was weakened by the following Al implantation. The rapid consumption of Nb and fast inward diffusion of O finally contributed to the poor long-term oxidation resistance of the Nb + Al implanted alloy.

Effects of C, Nb and C+Nb combined ion implantation on the oxidation resistance of γ-TiAl based alloy

The isothermal oxidation behavior of Ti–48Al–1.3Fe–1.1V–0.3B (at.%) implanted with C, Nb or C+Nb was investigated at 1173 K for 349.2 ks in air. Dose was 3.0×10 21 ions per m 2 and the acceleration voltage was 50 kV for each element. The purpose of this study is to improve the high-temperature oxidation resistance of the alloy by suitable implantation process and clarify the effects of C, Nb and their interaction on the formation of the oxide scale. Thermobalance, auger electron spectroscopy (AES) and scanning electron microscopy (SEM) were used to characterize the oxidation behavior and the scale structure. It was found that the C implantation is harmful to the long-term oxidation resistance, the Nb implantation significantly decreases the oxidation rate, and the C+Nb implantation can further improve the beneficial effect of the Nb implanted alloy and thus gives the best oxidation resistance. It was also found that for the C implantation, the C rich layer can act as a barrier to the inward diffusion of O in the early stage of the oxidation, but this effect will disappear after oxidation for about 3.6 ks due to the fast consumption of C. The presence of Nb can promote the formation of an Al enriched layer in the external scale. The co-existence of Nb and C would enhance their respective stability remained in the external scale or substrate with high peak concentration and thus prolong and intensify their respective beneficial effects. The significant improvement of the oxidation resistance of the C+Nb combined implantation is attributed to the above respective C and Nb beneficial effect and their interaction during the oxidation.

Oxidation behavior of TiAl protected by Si+Nb combined ion implantation

The combined ion implantation of Si+Nb at room temperature and at 1173 K with C contamination was employed to improve the oxidation resistance of a γ-TiAl based alloy [Ti–48Al–1.3Fe–1.1V–0.3B (at%)]. The implantation was conducted with a dose of 3.0×10 21 ions/m 2 and at an accelerate voltage of 50 kV for each element. The isothermal oxidation behavior of above treated alloys was tested at 1173 K for 349.2 ks in air. The oxide scales formed by short-term and long-term oxidation were characterized by AES, SEM and XRD. It was found that the alloy implanted with Si+Nb at 1173 K with C contamination shows excellent long-term oxidation resistance in comparison to that of the room temperature Si+Nb implanted alloy, although the latter also significantly lowers the oxidation rate of non-implanted alloy. A continuous, compact and thus a protective Al 2O 3 layer was formed in the scale of the alloy implanted with Si+Nb at 1173 K with C contamination after long-term oxidation, and this layer contributed to the best oxidation resistance. It is also indicated that the introduction of Si into Nb modified layer and, in particularly C in conjunction with Nb and Si in the modified layer can further effectively favor the formation of the continuous Al 2O 3 layer in the scale on alloy during high temperature oxidation.

Microstructure and Thermal Stability of Al2O3/Y3Al5O12 (YAG) Eutectic Composite Prepared by an Arc Discharge Method.

Eutectic composite of Al2O3/Y3Al5O12 (YAG) was prepared by an arc discharge method and its microstructure and stability were investigated. The eutectic composition of Al2O3/YAG determined by electron probe micro analysis (EPMA) was Al2O3:Y2O3=81.6:18.4mol%. Basic eutectic microstructure was a twinned single crystal of Al2O3 and YAG. The size of crystals was about 0.2-1μm in width. The fine eutectic microstructure about 0.4μm in width was oriented. The eutectic composite was stable at 1773K for 28.8ks in air, but resulted in grain growth at 1873K.

Fe-3 mass%SiO&lt;SUB&gt;2&lt;/SUB&gt;焼結体の高温酸化に対する水蒸気添加の影響

Oxidation properties of sintered Fe-3 mass%SiO2 (Fe-3SiO2) as well as Fe-1.5 mass%Si alloy (Fe-1.5Si) and Fe, for comparison, were investigated at 1273 K for up to 7.2 ks in air and air containing 10.5 vol%H2O (air-10.5H2O). In air-10.5H2O, the Fe-3SiO2 was oxidized faster than in air and also than the Fe-1.5Si in air-10.5H2O. The scale was composed of a duplex structure, an inner FeO+Fe2SiO4 and an outer Fe-oxides layers, where many voids existed in both layers. The similar scale structure containing voids was observed for the Fe-3SiO2 in air. Marker experiment with a small Pt wire was carried out for the Fe-3SiO2 oxidized in air-10.5 vol%H2O and the Pt-marker located between the inner and outer layers, suggesting that the inner layer grows due to inward migration of oxygen and the outer layer due to outward iron diffusion. In both air and air-10.5H2O Fe showed a parabolic oxidation, forming exclusively an outer Fe-oxides scale. It was suggested that SiO2, which changed to FeO+Fe2SiO4, acts as an obstacle for the outer layer recession, leading a formation of voids in the inner layer. Oxygen used to form the inner FeO+Fe2SiO4 layer was supplied by the dissociation of outer Fe-oxides, leaving voids, probably by a perforating dissociation mechanism. Both oxygen and water molecules could be diffusing species through the void.

Bi2223超伝導相とSr-V-O酸化物の界面反応

We have developed Ag-sheathed multifilamentary Bi2223 ((BiPb)2Sr2Ca2Cu3Ox) tapes with Sr6V2O11(SVO) barriers. The superconducting properties of the critical current density, Jc and a. c. losses of the tapes strongly depend on the purity of SVO, especially on the residue of SrCO3 in it. In order to examine the behavior of an SVO barrier in detail, we prepared pellet samples with seven layers, which were stacked by barrier and Bi2223 layers one after the other, and examined the reaction between them. The five kinds of barrier layers, such as SrCO3, Sr6V2O11(6-2SVO), 5 and 10 mass%V2O5-added 6-2SVO, and Sr3V2O8 (3-2SVO), were used. The pellet samples were heat-treated at 1113 K for 72-360 ks in air. In the barriers of SrCO3 and 6-2SVO, including the residue of SrCO3, the large Bi2212 (Bi2Sr2Ca1Cu2Ox) grains are grown perpendicular to the interface to form the Bi2212 layers with a thickness of about 100 μm by the reaction between the barrier and Bi oxide. The majority of the Bi-oxide layers are composed of Bi2223 fine grains parallel to the interface. The thickness of the formed Bi2212 layers decreases when the content of SrCO3 in the barriers is decreased. In the reaction, SrCO3 reacts with the Bi oxides, and the elements of Pb and Cu diffuse and distribute homogeneously in the barrier layers. The residue of SrCO3 in 6-2SVO decreases obviously when the additional content of V2O5 is increased. In the 6-2SVO barriers with 5 and 10 mass% added-V2O5, only the very fine Pb oxide grains of (Sr, Ca)2PbO4 are precipitated in a row along the interface. No precipitation occurs for the 3-2SVO barrier. The 6-2SVO is stable, and the 3-2SVO is transformed into the 6-2SVO phase during the heat treatment. We can conclude that, for the use of 6-2SVO as a barrier, it is very important to remove the residue of SrCO3 in the 6-2SVO to prevent the formation of Bi2212 layers and, for that purpose, a small addition of V2O5 is effective.

Influence of Al film deposition and following treatment on the high temperature isothermal oxidation behavior of a γ-TiAl-based alloy

The isothermal oxidation behavior of a γ-TiAl-based alloy Ti–48Al–1.3Fe–1.1V–0.3B (at.%) at 1123 K for 360 ks in air, which was treated by a combination process of pure Al film deposition with a thickness of approximately 0.2 and 0.4 μm by IBAD and the following pre-diffusion treatment of 873 K/86.4 ks in vacuum, respectively, was studied. It was found that the Al film was transformed into a layer of TiAl 3 through the pre-diffusion process. The isothermal oxidation resistance of the γ-TiAl-based alloy was improved by this kind of treatment especially that with 0.2 μm thickness Al film showed a considerable enhancement effect. The thickness of Al film formed by IBAD is a key factor of this kind of treatment since the microstructure of the TiAl 3 layer transformed by the following pre-diffusion treatment strongly depends on it. It is concluded that the existence of a layer of TiAl 3 which is rich in Al could favor the formation of Al 2O 3 and therefore retarded the diffusion rate during oxidation.

Improvement of Oxidation-Resistance of &amp;gamma;-TiAl Alloy by High Temperature Nb and Al Ion Implantation

The Nb and Al ion implantation on a γ-TiAl based alloy of Ti-48Al-1.3Fe-1.1V-0.3B (at%) at different implantation temperatures of room temperature, 973 and 1173K were performed respectively, with the same dose of 3.0 × 10 21 ions/m 2 and the acceleration voltage of 50 kV. The influence of implantation temperature upon the element distribution in the modification layer and the isothermal oxidation behavior of Ti-48Al-1.3Fe-1.1V-0.3B (at%) at 1173 K for 349.2 ks in air were investigated. It is found that the thickness of the modification layer is significantly increased when the implantation temperature increased to 1173 K in the case of Nb implantation. As Al implantation temperature is raised, Al 2 O 3 is formed and the concentration of Al and Ti in the modification layer is strongly changed. The oxidation resistance of Nb and Al implanted alloys is enhanced as the implantation temperature increased and especially 1173 K Nb implanted alloy shows the best result. The improvement of the oxidation resistance of Nb implanted alloy is attributed to the outward diffusion of Al resulting in the formation of Al 2 O 3 in the oxidation scale and this chemical effect of Nb doping can be further enhanced by high temperature implantation. The formation of Al 2 O 3 in the modification layer during the process of high temperature Al implantation is the main reason for the lower mass gain of high temperature Al implanted alloy. In addition, the reduction of the lattice defect and the stability enhancement of the doping element stayed in modification layer of high temperature implanted alloy are also responsible for the improvement of the oxidation resistance.

TiAl基合金の流動層処理による高温耐酸化性の向上

TiAl-base alloys are expected to substitute conventional materials for exhaust parts of automobile engines, because they have lower density and higher specific strength at elevated temperatures than heat resistant steels and Ni-base superalloys. The major key to successful application of TiAl alloys is improvement of oxidation resistance at high temperature.A new surface treatment using a fluidized bed with WO3 powder has been developed. The reagent used was a mixture of 40 mass%WO3 powder (100-200 mesh) with 60 mass%Al2O3 powder (80 mesh). The bed was fluidized by an argon gas flow. Specimens were treated in the bed at 1273 K for 7.2 ks. The oxidation tests were carried out at 1173 K and 1223 K for 720 ks in air and in a typical exhaust gas atmosphere. The mass changes were examined, in addition to the characterization of treated and oxidized surface using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Auger Electron Spectroscopy (AES).The cyclic oxidation resistance of TiAl-base alloys in air and exhaust gas up to 1223 K was significantly improved. The excellent oxidation resistance obtained is attributable to a continuous and sound Al2O3 surface layer formed during the treatment. This protective layer acts as a barrier against the formation of a complex oxide scale consisting of a TiO2 layer and a porous inner layer of TiO2 and Al2O3. The new surface treatment gives an oxidation resistance superior to that of the Ni-base superalloy Inconel 713C up to 1223 K.

Improvement of the Adhesion of a Ceramic Coating on a Ceramic Substrate

The structure and adhesion of an alumina coating on a ceramic substrate with NiCrAlY alloy bond coating was investigated by heating at 1573 and 1673 K in the air. Phases of NiO, NiCrO3, NiAl2O4, αAl2O3, and Ni were revealed in a 100 μm thick bond coating on heating at 1573 and 1673 K. A veined structure was also detected in the coating heated at 1573 K. The adhesion strength of the coating was improved and reached approximately 20 MPa on heating at 1573 and 1673 K for 14.4 ks in air although the strength of the as-sprayed coating was only 2 MPa. The improvement of adhesion strength may arise from the formation of NiAl2O4 with a spinel structure at the interfaces of the top coating/bond coating/substrate coating system. The adhesion strength of the coating improved on decreasing the bond coating thickness and reached approximately 45 MPa for a 20 μm thick bond coating which was heated at 1673 K. Only NiAl2O4 oxide was formed in the bond coating.

磁石・半導体 不可逆減磁率の改善された低Ｎｄ系希土類ボンド磁石

Isotropic bonded magnets made of rapidly quenched Nd-Fe-B powder (MQP-B powder) are widely used in various applications because of their superior magnetic properties and shape flexibility. However, it is not so easy to obtain fully magnetized magnets when a multipole magnetizing is necessary. Bonded magnets made of row rare-earth Nd-Fe-B powder (MQP-Q powder) show superior magnetizability to that of those made of MQP-B powder, because of the lower value of Hci . Therefore, the magnets seem to be suitable for applications where full magnetization is difficult. However, the irreversible flux losses of the bonded magnets made of MQP-Q powder are higher than that of bonded magnets made of MQP-B powder. Therefore, it is necessary to improve the irreversible flux loss in order to adapt these magnets to various applications. The effects of Nb addition on magnetic properties and irreversible flux loss were studied on bonded magnets with composition of Nd8Fe86-xB6Nbx , where x= 0 - 3. An irreversible flux loss was measured at Pc = 2 after exposure at 393 K for 3.6 ks in air. It was found that the Nb addition of 2 at.% or more decreased the irreversible flux loss. The value was less than 5 %, similar to that obtained with MQP-B magnets. B r decreased with the increase in Nb content. The effect of Nd content on the magnetic properties and irreversible flux loss was also studied on the bonded magnets with compositions of NdxFe92-xB6Nb2 , where x = 6 - 8. The bonded magnet with the optimum composition of Nd6.5Fe85.5B6Nb2 had Br similar to that of MQP-Q magnets that did not contain Nb, and the value of irreversible flux loss was comparable to that of MQP-B magnets. A multipole magnetizability test on the bonded magnets with the above optimum composition was