Effects of phosphorus on creep behaviour of nickel and Ni–20Cr and on creep and strength of Nimonic 80A

Abstract

The influence of P on the creep behaviour of Ni, Ni–20Cr (wt-%), and Nimonic 80A was investigated by carrying out creep tests under various loads and at different temperatures. After creep fracture the samples were investigated using optical, scanning electron, and transmission electron microscopy. The grain boundary segregation was examined using Auger electron spectroscopy (AES). It was found that P segregates to the grain boundaries in all the materials investigated. The creep rate of Ni–20Cr and Nimonic 80A is decreased by the addition of P. Grain boundary segregation of P and its influence on strength was also investigated using AES for specimens aged between 600 and 700°C after fracture by a tensile test inside an ultrahigh vacuum chamber. Maxima of tensile strength are observed to be time dependent as a result of carbide precipitation, which is affected by the P segregation.

MST/1679     

Effect of Notches and Environment on Cyclic Life of Alumina

Four-point bending cyclic fatigue testing has been performed for alumina specimens with two kinds of notch radius in corrosive environments. Cyclic life is found to be dependent on notch radius and environments, the tests also show that the fatigue notch factor Kf is roughly equal to the theoretical notch factor Kt, the fatigue strength and fatigue limit σc are reduced in environment in the sequence: formamide-room air-distilled water     

Wetting characteristics of sodium on β″-alumina and on nasicon

The sessile drop technique was used to determine the wetting characteristics of liquid sodium on -alumina and nasicon (Na₃Zr₂Si₂PO₁₂). The effects of moisture and temperature were studied using the wetting experiments. A range of contact angles (from 0 to 160°) were observed. The samples exposed to moisture exhibited poor wetting. The fact that good wetting is a prerequisite for improved cell performance was demonstrated via Na ¦-alumina¦ Na cell tests. Cells baked out in a vacuum passed in excess of 1100 Ah cm^–2 at 4 A cm^–2 current density without any degradation. Unbaked cells under similar conditions failed under 200 Ah cm^–2.     

Influence of microstructure on strength and fracture toughness ofβ-Sialon

-Sialon (Si_6–z Al _z O _z N_8–z ) withz = 0.5 was fabricated by hot-pressing of a spray dried mixture of –Si₃N₄ and aluminium-isopropoxide solution. Phase composition, flexural strength and microstructure of a sintered body were investigated. Phases identified by XRD were -Sialon and a small amount of O-Sialon. The flexural strength (three-point bending) was about 1500 MN m^–2. This value, about three times higher than that of -Sialon fabricated from -Si₃N₄ and -Al₂O₃ powder, was mainly due to the homogeneous microstructure without large defects such like clusters of large grains. -Sialon was heat treated at 2000 °C for 2 h in 4 M Pa N₂ to develop elongated -Sialon grains with high aspect ratio. Microstructure, flexural strength and fracture toughness (K _Ic) of it were investigated. Both strength andK _Ic were lower than those of hot-pressed sample, even though an elongated microstructure was achieved. This fact showed that the toughening of -Sialon with elongated grains could not be achieved without grain boundary phase which resulted in a crack deflection.     

Effect of Ga on Magnetic and Microstructural Properties of Nd-Fe-Co-B Alloys

1.IntroductionIn this work Ga and Co were added inthe Nd-Fe-B alloys to increase the Curietemperature and improve the temperaturedependence.The improvement of alloy per-formance and the mechanism of coercivitywith the additions of Ga and Co elementsare reported.The Curie temperature of the     

Effect of Sn on the Color and Tarnishing of Cu-Mn-Zn Alloys

The effect of Sn on the color and tarnishing of Cu-Mn-Zn alloys is investigated quantitatively. Using the CIE LAB color system, color parameters such as L*, a* and b* are selected to describe the surface color of alloys while the color difference (ΔE*) is used to evaluate the color stability. The results show that with the increase of Sn, the color change of Cu-Mn-Zn alloys is greatly reduced and the corrosion resistance in the synthetic sweat is improved dramatically. However, up to 4.4 wt pct Sn does not change the color of Cu-Mn-Zn alloys much. XPS and AES are employed to analyze the tarnished surface. It is proved that a Sn enriched film is formed and Sn takes the form of Sn oxide. This thin and protective oxide film can prevent alloy from further tarnishing.     

Influence of retrogression and reaging on microstructure and properties of 8090 Al–Li alloy

Abstract

An investigation was made into the influence of a retrogression and reaging treatment on the microstructure, tensile properties, and stress corrosion cracking resistance of 8090 Al–Li alloy. The results show that retrogression of the material at 230°C for 40 min or 325°C for 1·5 min, and then reaging to the peak aged condition, can result in an improved combination of tensile strength and stress corrosion cracking resistance. Through retrogression and reaging treatment, the alloy almost achieves the strength of the peak aged state and the stress corrosion cracking resistance of the overaged state. Transmission electron microscopy indicates that the δ′ phase dissolves during retrogression and reprecipitates during reaging, thus increasing the strength. The T₂ phase precipitates and grows during both retrogression and reaging, which results in the increase of stress corrosion cracking resistance.

MST/1670     

Effect of addition of tin on the microstructure and machinability of α-brass

This study was aimed at developing lead-free brass alloys with the goal of substituting lead element with tin. For this purpose, lead-free alloys with tin were developed and the microstructure, hardness and machining behaviour of the Cu–30%Zn alloy was compared with Cu–30%Zn–x%Sn (x?= 1.2, 3.2, 5.4, 8, 11.4, 13.9, 17.4). The results showed that the addition of Sn to single-α phase brass led to the formation of duplex (α?+?β′) brass and then the formation of (β′?+?? ) brass both with increased hardness. In addition, the addition of Sn to Cu–30%Zn alloy led to the decrement of equivalent machining forces (F_m), surface roughness and also the promotion of chip fragmentation due to the formation of the β′ phase, which is an improvement in machinability.     

Effect of crystal and domain orientation on the visible-light photochemical reduction of Ag on BiFeO₃

The reduction of silver from an aqueous solution on BiFeO? surfaces, activated by visible light, was investigated as a function of crystal and ferroelectric domain orientation. When excited by light with energy between 2.53 and 2.70 eV, BiFeO? photochemically reduces silver cations from solution in patterns corresponding to the underlying ferroelectric domain structure. Silver is preferentially reduced on domains with a positive polarization directed toward the surface. The amount of reduced silver depends on whether the component of the domain polarization normal to the surface is positive or negative, but is relatively insensitive to the crystal orientation. It is concluded that the ferroelectric polarization decreases electron drift to the surface in domains with a negative polarization, causing spatially selective photochemical behavior, and that the direction of the polarization is more important than the amplitude.     

Comments on ‘Effect of obstacle strength and spacing on the slope of Haasen plot’

In a recent paper, Mishra et al. [Effect of obstacle strength and spacing on the slope of Haasen plot. Mater Sci Technol. 2019;1–6. doi:10.1080/02670836.2019.1567043], discrepancy between theoretical and experimental results in the slope of the Haasen plot between pure metals and alloys were reported. The discrepancy arises from a common belief that when Haasen plot for pure metals is extended to metals with multiple strengthening mechanisms, the inverse of activation volume components can be linearly superposed. It is conjectured that the slope of the Haasen plot should remain the same for both the pure metals and alloys, as it is governed only by dislocation–dislocation interaction. The purpose of this note is to clarify that the conjecture of invariant Haasen slope is only a special case.     

Effects of temperature and dispersants on the phases and morphology of Ag–Cu nanoparticles

Ultrafine Ag–Cu nanoparticles (NPs) have been synthesized by a rapid one-step reduction within only 10 min. Effects of temperature and dispersants on the phases and morphology of Ag–Cu NPs were investigated. Results showed that citric acid exhibited an advantageous nature to avoid the formation of Cu₂O and form uniform morphology over PVP. The average particle size of the Ag–Cu NPs synthesized simply in ice-cubes bath could be controlled in 8.6 nm about a quarter of that synthesized at room temperature. The synthesized Ag–Cu NPs presented alloy states near the eutectic composition of 72:28. Due to the lower Ostwald ripening rate and citric acid protection, smaller Ag–Cu NPs were achieved in ice-cube bath. Results also showed that the ultrafine Ag–Cu NPs could be expected to sinter at about 330 °C which was much lower than the eutectic temperature (779 °C) of bulk Ag–Cu alloy. The ultrafine Ag–Cu NPs could be applied as potential die attach materials for SiC power devices.     

Promulgation and Implementation of National Standard on Diamond Grading

With the development of the diamond market, a revision of the national standard, Diamond Grading, formulated in 1996, was promulgated on Ju-ly 1, 2003 and became effective since Nov. 1, 2003. The revision was formulated based upon GB/T16554-1996, GB/T18303 and a large amount of domestic and international data and information to serve the purpose of improving the technical standard of diamond grading, accelerating the domestic mar-ket's entry the international diamond market as well as prote…     

The Diagnosis and Analysis of Crack on Automotive Gearbox

This paper concerns an experimental vibration analysis on the crack that appeared early on an automobile gearbox.We conduct the testing vibration analysis and modal analysis of the gearbox when the whole auto is in a coupling state,We conduct the testing vibration analysis when the auto is in a running state,and obtained the natural frequency and vibration modal of the gearbox in a vertical direction.The influence of imbalance to vibration amplitude of the gearbox at commonly used running speed and rotating speed is measured and analyzed,The influence of a rigid absorber is discussed too. After the dynamic strength of the gearbox was measured and analyzed,we determined the weak part of the gearbox and found every kind of influence factor for the gearbox break.     

Effect of δ-ferrite co-existence on hot deformation and recrystallization of austenite

This work evaluates the effect of co-existence of a large volume fraction of δ-ferrite on the hot deformation and dynamic recrystallization (DRX) of austenite using comparative hot torsion tests on AISI 304 austenitic and 2205 duplex stainless steels. The comparison was performed under similar deformation conditions (i.e. temperature and strain rate) and also under similar Zener-Hollomon, Z, values. The torsion data were combined with electron backscatter diffraction (EBSD) analysis to study the microstructure development. The results imply a considerable difference between DRX mechanisms, austenite grain sizes and also DRX kinetics of two steels. Whereas austenitic stainless steel shows the start of DRX at very low strains and then development of that microstructure based on the necklace structure, the DRX phenomena in the austenite phase of duplex structure does not proceed to a very high fraction. Also, the DRX kinetics in the austenitic steel are much higher than the austenite phase of the duplex steel. The results suggest that at a similar deformation condition the DRX grain size of austenitic steel is almost three times larger than the DRX grains of austenite phase in duplex steel. Similarly, the ratio of DRX grain size in the austenitic to the duplex structure at the same Z values is about 1.5.     

Effect of Different Rare-Earth on Microstructure and Properties of α-Sialon Ceramics

Densified Yb-, Y-, Dy-, Sin- and Nd-α-Sialon ceramics were prepared by two-step hot sintering. The variation of microstructure and properties with different rare-earth was investigated. The ceramics doped with smaller cations （Yb3＋, y3＋ and Dy3＋） are fully composed of α-Sialon, while in the larger cations （Sm3＋ and Nd3＋） doped ceramics also exist a few intergranular phase Mt （Re2Si3-xAlxO3＋xN4-x） in triple-point pockets. With increasing the radius of the rare-earth cations, the elongated α-Sialon grains form instead of the equiaxed grains in Yb-α-Sialon, and the aspect ratio of grains increases. All the ceramics possess high hardness, and the value of 21 GPa is achieved for Yb- and Y-α-Sialon. With increasing the ionic size of rare-earth, the hardness decreases slightly but the toughness tends to increase. Nd-α-Sialon possesses the highest toughness with the value of 5.4 MPa·m^1/2.     

Influence of damage on ultrasonic velocity and strength—analysis and experiments

Measurements of ultrasonic velocity in creep damaged material are reviewed. The influence of damage on ultrasonic velocity is analysed and the relation between them is derived. It is shown that measurements of ultrasonic velocity can be used to predict the remaining life. Measurements of ultrasonic velocity in a damaged beam are presented along with measurements of the ultimate strength. A relation is found to exist, between reductions in ultrasonic velocity and ultimate strength, which might be used to assess the load carrying capacity of a structural element.     

Influence of Alternative Magnetic Field on the Diffusion of Al and Mg

The influence of an alternative magnetic field on the diffusion of Al and Mg in AI-Mg diffusion couple is studied. The diffusion zone is composed of two intermediate phases, namelyβ and γ phase. Thickness of each intermediate phase is examined. The results show that the alternative magnetic field increases the thicknesses of βand γ phase zone and the layer growth ofβ and γphase obeys the parabolic rate law. The growth rate of the β and γ phase are increased with the application of the alternative magnetic field. This change is manifested through a change in the frequency factor k0 and not through a change in the activation energy Q. The frequency factor k0 for intermediate phase growth with an alternative magnetic field is 39.95 cm2/s for 7 phase and 2.84×10-4 cm2/s for β phase compared with those without the magnetic field is 22.4 cm2/s for 7 phase and 1.53×10-4 cm2/s for β phase.     

Effects of Nitridation on Properties of SiC Fiber and Interface of Ti Matrix Composite

Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can from more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix.The effect of nitridation on the tensile strength of the fiber was investigated in this work.Nitridation could degrade the tensile strength of the SiC if the treating temperature and time are not optimized.The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are respornsible for the degradation in strength.The strength can be maintained by further optimization of the treating temperature and time.Therefore stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical application.     

Effect of Thickness on the Structure and Tribological Properties of MoSx Coating

MoSx coatings were prepared by bipolar-pulse DC unbalanced magnetron-sputtering system with the variation of coating thickness at different Ar pressures.The composition and surface morphology were determined by using energy dispersive X-ray and scanning electron microscopy;the structural characterization was analyzed by X-ray diffraction.The friction and wear properties were investigated by fretting tests in air with less than 10% and 50% relative humidity.At 0.40 Pa pressure,(002) basal plane orientation was formed throughout the coatings.At 0.88 Pa and 1.60 Pa pressures,(002) basal plane orientation was only noticed in the first stage of coating growth(around 0.20 μm in thickness), and then edge orientations with their basal planes perpendicular to the surface would be evolved in the coatings.Humidity has a minor influence on the coatings that have(002) basal plane orientation,whereas the tribological properties of MoSx coatings with edge orientations are greatly affected by humidity.The mechanisms of coating growth and friction and wear processes are discussed.