Editorial: Surface coating in metal and metal alloy for anti-corrosion

High temperature ternary Ti50Ni25Pd25 and quaternary Ti50Ni20Pd25Cu5 shape memory alloys were developed in vacuum arc melting furnace using high purity constituent elements. Half numbers of samples were solution treated at 900 °C for 2 hrs and remaining were aged at 600 °C for 3 hrs. Both alloys were characterized for microstructure analysis and mechanical properties. After aging the alloys, no significant change in microstructure was observed in ternary alloy however, fine precipitates of bright color were found along the grain boundaries in quaternary alloy. The mechanical properties of ternary and quaternary alloys were found to be improved significantly. Microhardness of ternary alloy was increased by 18 Hv whereas for quaternary alloy the same property was improved by 24 Hv. Yield stress of ternary and quaternary was observed to be enhanced by 10 MPa and 9 MPa respectively. Similarly the fracture stress was observed to be increased by 9 MPa and 13.4 MPa. Conversely, the fracture strain of ternary and quaternary alloys was reduced by 0.5% and 0.35% respectively. From these results it can be established that aging at 600 °C is beneficial to improve the mechanical properties of both alloys however, quaternary alloy responded more actively as compared to ternary alloy.

The modified sessile drop method (MSDM) and the modified pycnometric method (MPM) have been employed to measure precisely the densities of liquid nickel-based ternary (Ni-Co-Al) and quaternary (Ni-Co-Al-Cr, Ni-Co-Al-Mo, Ni-Cr-Al-Mo) alloys and four commercial superalloys in liquid and mushy states. There was a good agreement between the values measured by the two methods. The measured densities of liquid model alloys and commercial superalloys in liquid and mushy states decreased linearly with increasing temperature for the experimental temperature range. The temperature coefficient of the density of liquid ternary Ni-Co-Al alloys measured in this work can be represented as a quadratic function of the aluminium concentration in the alloys. The density of liquid Ni-Co-Al alloys can be expressed as a function of both temperature and aluminium concentration in the alloys. The recommended equations for the densities of liquid nickel-based ternary and quaternary alloys and four commercial superalloys in liquid and mushy states were obtained by analysing density values measured by both MSDM and MPM. The calculated values from the recommended density equations show good agreement with those measured by both MSDM and MPM. The density (� ) and its temperature dependency (d�= dT) are important input data for simulation of the solidification of Ni-based superalloys, e.g. the prediction of defects such as gas porosity and microsegregation, as well as the evaluation of the convective contribution to heat transport. Accurate experimental values of the densities of nickel and Ni-based model and commercial alloys (including their dependencies on composition and temperature) are needed to develop models to predict the densities of Ni-based superalloys. In order to predict the densities of Ni-based commercial alloys, it is necessary to have an understanding of the effects of the various alloy elements (such as Cr, Co, Ta, W, Al, Mo, Re, Hf, Nb, Ti, etc.) on the densities of liquid nickel alloys. This can be obtained from accurate measurements of the densities of Ni-based binary alloys in relation to the concentration and temperature. Comparisons of the densities of liquid Ni-based ternary alloys with those for the corresponding binary alloys provide useful information on the effects of the second alloy element on the properties of liquid alloys. For some alloy elements, such as Re, their concentrations in the Ni-based superalloys are relatively low but they are very reactive, which may make the accurate density measurement of their Ni-based binary alloys difficult. The effect of these elements on the densities of Ni-based superalloys can be obtained by comparing the densities of liquid Ni-based commercial alloys with those of liquid Ni- based multi-component model alloys with similar chemical compositions to those of the Ni-based commercial alloys. Furthermore, accurate density values of both Ni-based model and commercial alloys can be used to verify the validity of the models developed to predict the densities of liquid Ni- based superalloys. However, there is a large scatter in the reported density values for liquid nickel and its temperature dependence because of the experimental uncertainties associated with the different techniques. Furthermore, there are very few reports on the measurement of the density of Ni-based alloys in relation to the effects of composition and temperature. 1-7) There are no reports on the measurement of the densities of liquid Ni-based multi-component model alloys such as ternary and quaternary alloys. Therefore, in order to develop a model to predict the densities of commercial Ni-based superalloys, we have used two accurate methods, namely, the modified sessile drop method (MSDM) and the modified pycnometric method (MPM) to measure the densities of liquid nickel and Ni-based model alloys and commercial alloys in the liquid state and in the mushy (ie ''liquid-solid coexistence'') state for some alloys. The principles, advantages and experimental proce- dures of the two methods have been described previously. 5-7) The densities of liquid nickel and liquid Ni-Cr, Ni-Co, Ni-Ta, Ni-W and Ni-Al alloys have been measured precisely with both methods, and density values for Ni-Cr and Ni-Al alloys in mushy state have also been determined. 5-7) In this paper, both MSDM and MPM were employed to measure the densities of liquid ternary model alloys (Ni-Co- Al, molar fraction xNi:xCo � 86:14, Al mass% = 0� 11), liquid quaternary model alloys (Ni-Co-Al-Cr, Ni-Co-Al-Mo and Ni-Cr-Al-Mo), and four commercial Ni-based super- alloys in liquid and mushy states. The chemical compositions of these model alloys were similar to those of commercial Ni- based superalloys. The recommended density values for these alloys have been obtained by combining the measured values determined with the two methods.

Development and characterization of highly formable magnesium sheet alloys

Annual Report: Fuels (30 September 2012)

The damping characteristics of Ti50Ni49.5Fe0.5 and Ti50Ni40Cu10 ternary shape memory alloys (SMAs) have been systematically studied by resonant-bar testing and internal friction (IF) measurement. The damping capacities of the B19′ martensite and the B2 parent phase for these ternary alloys are higher than those for the Ti50Ni50 binary alloy. The lower yield stress and shear modulus of these ternary alloys are considered to be responsible for their higher damping capacity. For the same ternary alloy, the B19/B19′ martensite and R phase also have a higher damping capacity than does the B2 parent phase. In the forward transformations of B2 → R, R → 519′, and B2 → 519′ for Ti50Ni50 and Ti50Ni49.5Fe0.5 alloys, the damping capacity peaks appearing in the resonant-bar test are attributed to both stress-induced transformation and stress-induced twin accommodation. The lattice-softening phenomenon can promote the stress-induced transformation and enhance the damping capacity peaks. The Ti50Ni40Cu10 alloy had an unusually high plateau of damping capacity in the B19 martensite, which is considered to have arisen from the easy movement of twin boundaries of B19 martensite due to its inherently very low elastic modulus. The peaks appearing in the IF test for the Ti50Ni40Cu10 alloy are mainly attributed to the thermal-induced transformation due to T ⊋ 0 during the test.

The Thermodynamic Characterization of ZrCo–H, HfCo[sbnd]H, HfNi[sbnd]H and Zr1–xHfxNi(Co) Alloy–H Systems

This study aims to investigate the microstructure, creep behavior and high temperature oxidation behavior of novel high niobium-containing Ti-40Al-xNb (x=10,12,15,16) intermetallic alloy. The microstructure of the as-cast Ti-40Al-10Nb alloy consists of dense Widamanstatten α2 laths in the B2 matrix. The microstructure of the as-cast Ti-40Al-xNb (x=12,15,16) alloy is composed of the primary β dendrites and dense γ phases with various morphologies, such as lathy, feathered and irregular shapes. Following heat treatment, the microstructure of the heat-treated Ti-40Al-10Nb alloy resembles that of the as-cast Ti-40Al-10Nb alloy. The homogenized Ti-40Al-12Nb alloy and Ti-40Al-15Nb alloy have a two-phase microstructure of B2+γ, while the homogenized Ti-40Al-16Nb alloy has a four-phase microstructure of B2+γ+α+σ.The microstructure of the as-cast Ti-40Al-16Nb-0.4wt% X (X=Sc or Mm) alloy contains many Sc-rich oxides with cubic or cauliflower-shapes and La2O3 oxides having strip-like or spherical shape in the inter-dendrite region. The formations of these precipitates are caused by the internal oxidation during solidification. After homogenization, numerous fine particles with sub-micrometer scale are present in the Ti-40Al-16Nb-0.4wt% X (X=Sc or Mm) alloy. This is due to the fact that during long-term heat treatment at high temperature, Sc or Mm elements, initially dissolving in the as-cast alloy, may react with oxygen atoms by internal oxidation and reproduce fine-scale particles. The creep responses of the Ti-40Al-xNb (x=15,16) alloy are strongly correlated with tertiary creep behavior. The deformation of creep converges mainly at the B2 phase. A stress exponent of 4.5 estimated indicates that the mechanism of controlling creep behavior is dislocation climb. The creep curve of the Ti-40Al-xNb (x=15,16) alloy does not exhibit a steady-state region, resulting from the absence of the subgrain structures of dislocations in the alloys during secondary creep. The creep activation energy of the Ti-40Al-xNb (x=15,16) alloy is about 365 KJ/mole. The calculated values of activation energy for the alloys are quite close to the activation energy of Ti self-diffusion in the β phase (~353KJ/mole). The creep fracture of the alloys is dominated by cleavage fracture over the entire fracture surface. The brittleness of the σ phase causes most of the cracks to run through it immediately, indicating no resistance to their propagation. Therefore, the creep life of the Ti-40Al-16Nb alloy is shorter than that of the Ti-40Al-15Nb alloy. The strengthening effects of minor elements added (Sc or Mm) are apparent on the properties of tertiary creep rate and rupture life of the alloys. The fine particle formed after homogenization is an effective obstacle to the motion of dislocations, further increasing the creep fracture life of the alloys. The fracture of the Ti-40Al-xNb (x=15,16) and Ti-40Al-16Nb-0.4wt% X (X=Sc or Mm) alloy during tertiary creep is caused by microstructural instabilities. The results of the isothermal oxidation tested at the temperature of 800℃ for the Ti-40Al-xNb (x=10,12,15,16) alloys reveal that the difference among the oxidation resistances of these four alloys arise from their various microstructures. The oxidation resistance of α2 is inferior to that of γ. At a higher temperature of 900℃, the effect of Nb content on the oxidation resistance of the Ti-40Al-xNb (x=10,12,15,16) alloy becomes more pronounced. For the Ti-40Al-xNb (x=10,12,15,16) alloys, the increased Nb content promotes the formation of Al2O3 oxides. Therefore, the Ti-40Al-15Nb alloy has the strongest oxidation resistance among these four tested alloys. But at 1000℃, the Ti-40Al-xNb (x=10,12,15,16) alloys show a severe scale spallation, indicating that these alloys could no more resist the oxidation and lost their surface protection at the temperature.

Microstructural characterization of Mg-Y-Zn based alloys

Application of molecular interaction volume model for predicting the Ca activity coefficients in Si[sbnd]Ca binary and Si[sbnd]Ca[sbnd]Pb ternary alloys

Thermal stability and hardening behavior in superelastic Ni-rich Nitinol alloys with Al addition

Introduction: Dental alloys are routinely subjected to multiple casting procedures. Repeated casting of the same alloys may cause loss of trace elements (such as Sn, Si, Mn, etc.) that are essential for the metal ceramic bond. A common practice is to include a proportion of new metal with the previously cast metal that is thought to replenish the lost elements. Objective: The study was done to evaluate the effect of variation in percentage of recasted Ni-Cr alloy used and to compare the effects with the shear bond strength of porcelain to the fresh ingot Ni-Cr alloy. Materials and methods: Uniform patterns were fabricated, invested and casting was done in five different combinations of fresh and recast alloy. A hundred percent fresh alloy; 25% recast with 75% fresh alloy; 50% recast and 50% fresh alloy; 75% recast and 25% fresh alloy; 100% recast alloys. After uniform porcelain application and firing, the specimens were subjected to shear bond test using a universal testing machine. Data were statistically analyzed using Duncans’s multiple comparison test. Results: The results showed that the mean shear bond strength of the 100% fresh alloy was maximum and 100% recast alloy was least among the groups tested. The mean shear bond strength of castings obtained from 100% fresh, 25% recast, and 50% recast alloy were similar to each other and showed statistically significant difference when compared to the 100% recast group. Seventy five percent recast group did not show statistically significant difference with 100% recast alloy. Arch Oral Res. 2011 May/Aug.;7(2)177-82 Rajalbandi SK, Kumar V, Sajjan S. 178 Introduction The Development of “Taggarts” technique of casting by lost wax process into the Dentistry gave an impetus to use alloyed metals as a restoration (1). Most of the dental laboratories commonly use the sprue and button from a previous casting as a part of the melt for the new casting (2, 3). This practice is especially detrimental with ceramometal alloys, which contain trace elements essential for bonding to porcelain. Repeated casting of these alloys may cause sufficient quantities of these elements to be lost so as to affect the bond between the metal and the porcelain (4-6). Studies have shown that recasting the used alloy up to 25% did not show any deleterious effects on the bond strength of porcelain (2). A combination of cast alloy with 50% new alloy produced the highest bond strength values. Further use of pooled alloy with an unknown casting history was not recommended since reduced bond strength were observed in their study (6). Among all the base metal alloys systems, the most popular are Ni-Cr Conclusion: It can be concluded that minimum of 50% fresh alloy for casting is a safe margin for recasting Ni-Cr alloy. s.

Stress corrosion cracking of Al-Zn-Mg-Cu alloys: effects of heat-treatment, environment,and alloy composition

To investigate effects of the leaching liquids of 5 different kinds of dental alloys on L929 cells at cell level and molecular level. The fibroblast L929 cells of mouse were cultivated in vitro in leaching liquids of 5 different kinds of dental alloys, Au alloy (n = 8), Ag-Pt alloy (n = 8), Co-Cr alloy (n = 8), Ni-Cr alloy (n = 8), and Cu alloy (n = 8). The RPMI 1640 cell medium containing 10% fetal beef serum was used as control. The cytotoxicities of the 5 dental alloys were evaluated by means of methyl thiazolyl tetrazolium (MTT), and the effects of these alloys on the expression of caspase-3, caspase-8, and caspase-9 mRNA of L929 cells were examined using reverse transcription polymerase chain reaction (RT-PCR) method. After 48 hours culture the cytotoxicity of Cu alloy group was in Grade 4 and those of the other groups were all in Grade 0. The mRNA levels of caspase-8 had no change in all groups (P > 0.05). The mRNA levels of caspase-3 were as follows: Cu alloy (0.474 +/- 0.001), the negative control (0.527 +/- 0.003), Au alloy (0.528 +/- 0.013), Co-Cr alloy (0.615 +/- 0.007), Ag-Pd alloy (0.673 +/- 0.009), and Ni-Cr alloy (0.803 +/- 0.037). The mRNA levels of caspase-9 were as follows: Cu alloy (0.532 +/- 0.041), Au alloy (0.574 +/- 0.013), the negative control (0.578 +/- 0.010), Co-Cr alloy (0.617 +/- 0.009), Ag-Pd alloy (0.703 +/- 0.018), and Ni-Cr alloy (0.811 +/- 0.037). There were significant differences between the groups except the negative control group and Au alloy group. The Cu alloy shows the highest cytotoxicity, and the leaching liquids of 5 different kinds of dental alloys may induce cell apoptosis through mitochondrion pathway.

Objective To study the antibacterial property and cytocompatibility of medical biodegradable zinc alloy in vitro. Methods Escherichia coli and Staphylococcus aureus strains were respectively mixed with LB culture medium, the concentration of 1.0×108CFU/mL was regulated by the bacterial turbidimetric instrument. The bacteria was cultured in carbon dioxide incubator of 37℃ for 24 h as bacteria original liquid. The same size of zinc alloy and titanium alloy (Ti6Al4V) rods were prepared for experiment, the surface oxide layer was polished and removed, which was cleaned ultrasonically in 100% ethanol and distilled water, disinfected with ethylene oxide, standby. (1) Escherichia coli/Staphylococcus aureus strains were respectively co-cultured in LB culture medium with biodegradable zinc alloy, titanium alloy. The absorbance value at the time of 0、2、4、6、8、12、24、48、72 h after cultured at 600 nm wavelength was determined by enzyme-linked immunosorbent assay.(2) Zinc alloy and titanium alloy were respectively placed on Staphylococcus aureus strains solid culture plates, bacteriostatic circles were observed at 24、48 h after cultured. (3) L929 cells were cultured with different concentrations of zinc alloy extracts, cell morphology were observed at the time of 1、5 d after cultured, CCK8 method was used to detect the cell proliferation and cell relative rate of increment(RGR) was calculated. (4)The MC3T3-E1 cells were seeded respectively on zinc alloy surface and titanium alloy to observed adhesion and growth state 2 days after cultured. Single factor analysis of variance (ANOVA) and t test were used to compare the data between the groups. Results The absorbance values of Escherichia coli and zinc alloy co-culture group were significantly lower than Escherichia coli culture group, Escherichia coli and titanium alloy co-culture group at different phase points, the differences were statistical significant(P values were less than 0.05). The absorbance values of Staphylococcus aureus and zinc alloy co-culture group were significantly lower than Staphylococcus aureus culture group, Staphylococcus aureus and titanium alloy co-culture group at different phase points, the differences were statistical significant(P value was less than 0.05). Bacteriostatic circles were observed near biodegradable zinc alloy, no bacterial colony appeared around (4.38±0.40)mm near the zinc alloy at 24 hours after cultured, while no bacterial colony appeared around (4.75±0.44)mm at 48 hours after cultured, no significant difference existed between the diameter of bacteriostatic circles (t=-1.10, P=0.31), no bacteriostatic circle was observed near the titanium alloy. The growth of L929 cells were good in the culture and negative control group with different concentrations of zinc alloy. CCK8 assay suggested that cell RGR in the leaching solution groups were more than 75%, the cell toxicity was 0-1 grade at different time points, the cytotoxicity of zinc alloys was safe and acceptable. MC3T3-E1 cells could grow and adhere on the surface of zinc and titanium alloy. There was no abnormalities compared with the titanium alloy group in cell morphology. Conclusion Zinc alloy material has good antibacterial activity against Escherichia coli and Staphylococcus aureus, and has good cellular compatibility, the cell toxicity is safe and acceptable, and cells can grow and adhere on the surface of it. Key words: Zinc alloys; Biodegradable implants; Antibacterial property; Cytotoxicity

A ternary TiNiCu shape memory alloy is subjected to high‐pressure torsion (HPT) followed by post‐deformation annealing (PDA) to study the effect of Cu (5 at%) on amorphization after HPT processing and to investigate the microstructural evolution and shape memory effect (SME) after PDA. The results show that even after 20 revolutions the ternary alloy contains nanocrystalline areas and the microstructure is not fully amorphous. An easier martensite‐to‐austenite transformation and minor remaining austenite in the ternary alloy are responsible for suppressing amorphization. Post‐deformation annealing at 673 K provides nanocrystalline microstructures containing an R‐phase with a minor martensitic B19' phase in the ternary alloy. The SME of this alloy after PDA is not as satisfactory as that of the binary alloy processed through similar conditions because of the existence of a high volume fraction of the R‐phase. However, the total recovered strain of the ternary alloy after PDA for 30 min has a maximum value of 6.5%.