Small Additions Of Ti Research Articles

Ordering effects on deformation substructures and strain hardening behavior of a CrCoNi based medium entropy alloy

A CrCoNi based medium entropy alloy with small additions of Ti, Al and Nb (denoted as (CrCoNi)93Al4Ti2Nb) in the as-quenched condition, exhibits tensile properties comparable to those of the equiatomic CrCoNi alloy at room temperature. Dark field transmission electron microscopy (TEM), atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) together with atom probe tomography (APT) show that spatially-localized long range ordering (LRO) L12 domains exist in this alloy. The evolution of deformation substructure with plastic deformation in this alloy was characterized using electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and STEM based techniques including the recently developed weak beam dark field STEM imaging. Plastic deformation occurs by the slip of a/2<110>dislocations, which are narrowly dissociated into Shockley partial dislocations on {111} slip planes. Their dissociation distances in the (CrCoNi)93Al4Ti2Nb alloy are much smaller than the widths of the corresponding partials in the equiatomic CrCoNi alloy due to one or more of the minor alloying elements (Al, Ti, Nb). Dislocation slip in this alloy has a pronounced planar character. The leading dislocations in slip bands glide as pairs due to the existence of LRO domains. Multipoles were formed through the slip of dislocations with opposite signs on adjacent {111} slip planes. Those multipoles serve as building blocks for the formation of subgrain structures consisting of fine slip bands. The distances between slip bands were continuously refined during plastic deformation and dynamic refinement of slip bands plays a crucial role in strain hardening. The effects of LRO domains on planar dislocation slip, the deactivation of deformation twinning and strain hardening of this alloy are discussed.

Effects of Ti content on the wetting behavior and chemical reaction in AgCuTi/SiO2 system

Effect of Ti Content on the wetting behavior and chemical reaction in AgCuTi/SiO2 system are studied. The results show that small additions of Ti in AgCu braze alloys can decrease the final contact angle θF, but the Ti content increases from 2.0 wt % to 7.8 wt %, the contact angle θ changes little. The additions of Ti in AgCu can obviously increase the work of adhesion, as Ti content increase to 2.0 wt %, 4.0 wt % and 7.8 wt %, the increased work of adhesion is 1080 mJm−2 (ΔW1), 1083 mJm−2 (ΔW2) and 1083 mJm−2 (ΔW3), respectively. However，the little changes of the increased work of adhesion for enhancing Ti content in braze alloys are responsible for the tiny change of the final contact angle θF. The results also show that as the Ti content increases, the microstructures in the wetting drop zone change. As the Ti content increases to (4.0, 7.8) wt. %, Ti5Si3 compounds are formed in the wetting drop, which decrease the activity of Ti leading to the little change in spread rate.

Influence of heat treatments on microstructure and pitting corrosion resistance of 15%Cr supermartensitic stainless steel

Supermartensitic is a new class of stainless steels in development and consolidation as commercial products. Significant changes on chemical composition of conventional martensitic stainless steels, such as the reduction of the carbon content to <0·03 wt-%, and the addition of Ni and Mo, marked the development of this new group of alloys. New grades containing higher amounts of Cr and small additions of Ti and/or Nb were developed recently. As a result, supermartensitic steels offer an interesting combination of high strength, toughness, weldability and corrosion resistance. In this work, the pitting corrosion resistance of a 15Cr supermartensitic steel with Ni, Mo and Cu additions was studied. It is well known that the mechanical properties and corrosion resistance of martensitic steels are adjusted by the final tempering treatment. Several single tempering treatments in the 300–650°C range and double tempering treatments were performed in order to obtain different microstructures. The pitting corrosion resistance was investigated by electrochemical test in 3·5%NaCl solution. It was found that the pitting potential slightly decreased with the increase in temperature and time of tempering. The analysis of pits formed during the corrosion tests showed that ferrite islands are more corrosion resistant than the martensitic matrix due to the higher Cr and Mo contents.

Local order and nanostructure induced by microalloying in Al–Y–Fe amorphous alloys

Extended X-ray absorption fine structure (EXAFS) measurements show that the dramatic improvement in glass formation in Al–Y–Fe alloys made with a small additions of Ti and V has a structural origin. The EXAFS spectra show that a well-defined Al atomic structure exists around the V and Ti atoms that is different from that around the major constituent Al, Y and Fe atoms, even at the lowest concentrations. The local Ti– and V–Al clusters have a size of about 1 nm. Around the V atoms, the local order can be described by a small face centered cubic cluster. Around the Ti atoms, the local structure seems to evolve from a face centered cubic nano-cluster towards a body centered cubic one when the concentration increases from 0.5% to 2%. These measurements demonstrate that Ti and V form strong interactions with Al, with a significant shortening of the bond length. This should raise the barrier for nucleation of α-Al, explaining the greater stability of the glasses containing Ti or V.

Grain refining of conventional and semi-solid A356 Al–Si alloy

The effect of inoculation has been studied on the microstructural evolution in conventional and semi-solid-metal (SSM) processing of A356 Al–Si alloy. It has been found that small additions of Ti–B shift the liquidus temperature up and the recalescence decreases. The nucleation event takes place at higher temperatures. Furthermore, the rate at which growth temperature increases is less than that of nucleation temperature and therefore more nuclei form with less potential for growth. In SSM processing refiner increases the α-Al percentage and reduces globule size. Improvement of primary particles’ sphericity and globule size reduction are the main advantages of refiner addition.

Precipitation in V bearing microalloyed steel containing low concentrations of Ti and Nb

The paper describes the precipitation behaviour in a thermomechanically processed V bearing microalloyed steel containing small additions of Ti and Nb (0·007–0·008 wt-%) using analytical transmission electron microscopy. An intriguing aspect is the significant precipitation of titanium and niobium at these low concentrations, contributing to strength. A high density of multimicroalloyed precipitates of (V, Nb, Ti)(C, N) are observed instead of simple TiN, TiC, and NbC precipitates. They are characterised as cuboidal (45–70 nm), spherical (20–45 nm), irregular (20–45 nm), and fine (10–20 nm). Estimation of solubility products of carbides and nitrides of V, Nb, and Ti implies that the precipitation of titanium occurs primarily in austenite. Interphase precipitation of niobium occurs during austenite to ferrite transformation, while complete precipitation of vanadium takes place in the austenite–ferrite region close to completion of transformation. Substoichiometric concentrations of Ti and Nb, the presence of nitrogen, and the mutual extensive solubility of microalloying carbonitrides explains the formation of core shell (triplex/duplex) precipitates with highly stable nitrides ((Ti, Nb, V)N) in the core and carbides ((Ti, Nb, V)C) in the shell. The qualitative stochiometric ratios of triplex and duplex carbonitrides were Ti0·53Nb0·35V0·12 and Ti0·6V0·4, Nb0·51V0·49 and Ti0·64Nb0·36. Extensive precipitation of fine carbides on dislocation substructures, and sub-boundaries occurred. They were generally characterised as vanadium carbide precipitates with ordered cubic L12 structure and exhibited a Baker–Nutting orientation relationship with the ferrite matrix. M4C3 types of carbides were also observed similar to the steel, having high concentrations of Ti and Nb.

Nanoscale precipitation in a maraging steel studied by APFIM.

This article summarizes findings from our previous investigations and recent studies concerning precipitation in a maraging steel of type 13Cr-9Ni-2Mo-2Cu (at.%) with small additions of Ti (1 at.%) and Al (0.7 at.%). The material was investigated after aging at 475 degrees C up to 400 h using both conventional and three-dimensional atom-probe analyses. The process of phase decomposition in the steel proved to be complicated. It consisted of precipitation of several phases with different chemistry. A Cu-rich phase was first to precipitate and Mo was last in the precipitation sequence. The influence of the complex precipitation path on the material properties is discussed. The investigation clearly demonstrated the usefulness of the applied techniques for investigation of nanoscale precipitation. It is also shown that, complementary methods (such as TEM and EFTEM) giving structural and chemical information on a larger scale must be applied to explain the good properties of the steel after prolonged aging.

Improved Al–Y–Fe glass formation by microalloying with Ti

We demonstrate that the sequence of phases formed upon annealing rapidly quenched Al88Y7Fe5 alloys is a sensitive function of the sample preparation conditions. Materials that show X-ray diffraction patterns typical of amorphous metallic alloys are actually partially nanocrystalline in some cases. Isothermal differential scanning calorimetry (DSC) studies of alloys with glass-like X-ray diffraction patterns demonstrate that an exothermic peak observed in non-isothermal DSC scans typically associated with glass crystallization is actually due to coarsening of nano-sized grains of α-Al. However, alloys prepared with small additions of Ti (Al88- x Y7Fe5Ti x with x = 0.5, 1 or 2) are amorphous. The crystallization temperature increases with increasing concentrations of Ti. Experimental data indicate that Ti is not simply a scavenger of internal O but may enhance local ordering in the undercooled alloy, stabilizing the liquid against the nucleation of the α-Al phase.

Primary crystals in ZrTiCuNiBe bulk glasses

ZrTiCuNiBe glasses can be prepared in massive form by quenching of the liquid melt with a cooling rate of about 10 K s−1. During cooling down of the melt a small fraction of primary crystals in the glassy matrix is difficult to avoid. Morphology, microstructure and chemical composition of these primary crystals have been investigated by optical microscopy, transmission electron microscopy (TEM) and TEM-EDX. Two types of crystal morphology were observed, dendritic and prismatic. TEM-EDX analysis (which cannot detect Be) indicate that these two types of crystals have similar composition. TEM diffraction of the prismatic crystals revealed an ordered orthorhombic structure with lattice parameters of a=0.37 nm, b=0.66 nm, c=0.63 nm. The true composition of the prismatic crystals and the matrix was determined by FIM/AP-analysis. This analysis revealed a composition of the prismatic crystals according to ZrBe2 with small additions of Ti, Cu and Ni.

The Effects of Ti and S in Direct Rolled Thin Slab Cast Low Carbon Steel

The effects of sulphur on the metallurgy of mild steel produced via the Thin Slab Direct Rolling (TSDR) and Cold Charge Rolling (CCR) routes were compared. Particular attention was given to the precipitation behaviour of MnS and its influence on the microstructure, mechanical properties and susceptibility to cracking of the hot band. The sulphur content was varied from 0.003wt% to 0.04wt% and three levels of Mn (0.10, 0.24 and 0.64 wt%) were used. A number of casts with Ti additions of 0.024 and 0.036wt% were also made. CCR produced an homogenous, polygonal grain structure while TSDR product displayed banding of the microstructure into coarse and fine ferrite grains. The banding was less severe at low S contents. The average grain size of the TSDR product became finer than that of the CCR product as the S content was increased. Yield strength was greater in the TSDR material and increased to a maximum at a sulphur content which was inversely related to the level of Mn. Mechanisms responsible for the observed change in mechanical properties with S content include ferrite grain refinement, due to botn the refinement of the austenite grain size through precipitation of MnS on the austenite grain boundaries, and strain induced precipitation of MnS during rolling, which retarded recrystallisation and increased retained strain prior to transformation. Surface defects in the form of edge cracking were observed in all TSDR strip with the general exception of low S and high Mn steels. The cracking was most severe in the low Mn TSDR steels where it occurred at very low S levels. It was found that an isothermal hold at 1150°C for 20 minutes prior to rolling eliminated cracking. The severity of the cracking appeared to be dependent on the amount of S in solution prior to rolling. Small additions of Ti significantly reduced the degree of edge cracking, due to the formation of a Ti-based sulphide and heterogeneous nucleation of MnS on Ti-based oxide particles.

The corrosion of Ni3Al in a combustion gas with and without Na2SO4-NaCl deposits at 600?800�C

The corrosion behavior of Ni3Al containing small additions of Ti, Zr, and B in combustion gases both with and without Na2SO4−NaCl deposits at 600–800°C has been studied for times up to four days. The corrosion of the saltfree Ni3Al leads to the formation of very thin alumina scales at 600°C but of mixed NiO−Al2O3 scales containing also some sulfur compounds at higher temperatures, while the rate increases with temperature up to 800°C. The presence of the salt deposits considerably accelerates the corrosion rate, especially at 600 and 800°C. The duplex scales formed at 600°C are composed mostly of a mixture of NiO and unreacted salt in the outer layer and of alumina and aluminum sulfide with some nickel compounds in the inner layer. The scales grown at 700°C contain only one layer of complex composition, while those grown at 800°C are similar but have an additional outer layer containing similar amounts of nickel and aluminum. At 600 and 700°C NiSO4 can be detected also in the salt layer. The samples corroded at 700°C and 800°C also show an Al-depleted zone containing titanium sulfide precipitates at the surface of the alloy. The hot corrosion of Ni3Al involves a combination of various mechanisms, including fluxing of the oxide scale as well as mixed oxidation-sulfidation attack. At all temperatures Ni3Al shows poor resistance to hotcorrosion attack as a result of the formation of large amounts of Ni compounds in the scales.

Creep of low-activated Fe-12Cr-20Mn-1W austenitic corrosion-resisting steel

1. Creep resistance of the Fe-12Cr-20Mn-1W steel, containing 0.1-0.26 wt. % C and also small additions of Ti, B, and P in the range 823–973 K is similar to the creep resistance of the Fe-Cr-NI steels of the 304 type, 800 alloy, and also the Fe-Cr-Mn-Ni steel of the EP838 type. 2. An increase of the carbon content in the range 0.1–0.26 wt. % in the Fe-12Cr-20Mn-1W alloys slightly reduces the minimum creep rate 873 K and does not effect this parameter at 973 K. 3. The efficiency of the effect of carbon on the minimum creep rate of the Fe-12Cr-20Mn-1W steels is evidently lower than the 800 alloy.

Characterization of chemically deoxidized liquid phase epitaxial GaAs

The deoxygenation of the gallium solvent by small additions of Ti or Zr in the liquid phase epitaxial (LPE) growth of GaAs was studied using an in situ electrochemical measurement technique. The oxygen activity in the liquid Ga melt was reduced in a few minutes from its steady-state value in a purified hydrogen ambient at 750°C by one or three orders of magnitude by the addition of Ti or Zr, respectively. The additions cause an increased tendency to produce high mobility p-type LPE GaAs. Photoluminescence, deep-level transient spectroscopy and secondary ion mass spectroscopy were used to establish the role of oxygen and the Ti or Zr additions in the compensation mechanism of the resulting LPE layers.

Superconducting critical temperatures, critical magnetic fields, lattice parameters, and chemical compositions of ‘‘bulk’’ pure and alloyed Nb3Sn produced by the bronze process

Superconducting critical temperatures Tc and magnetic fields Hc2, lattice parameters a0, and chemical compositions were measured for ‘‘bulk’’ layers (∼6 μm or greater) of ‘‘pure’’ and alloyed Nb3Sn which were made by the bronze process. The values of Tc, a0, and the composition of pure Nb3Sn layers were ∼18 K, 0.52900±0.00005 nm, and 25±0.5 at. % Sn, respectively, independent of heat-treatment temperature (between 650–780 °C) and of the bronze composition, as long as the thickness of the layers was greater than ∼6 μm. Small additions of Ti (∼1 at. %) or Ta (∼3 at. %) slightly increased the value of Tc (by ∼0.2–0.4 K) above that for pure Nb3Sn. However, additions of larger amounts of these elements or addition of other transition elements (V, Zr, and Mo) significantly decreased Tc. Also, small additions of these elements significantly increased Hc2. Specifically, the largest values of Hc2 (∼27 T at 4.2 K) were obtained for Nb3Sn layers containing ∼1.5 and ∼4 at. % of Ti and Ta, respectively, compared with a value for the pure Nb3Sn of 23.5 T at 4.2 K. The value of a0 decreased with all of the alloying additions; these variations can be explained qualitatively by several models for the lattice parameter of A15 compounds, but none of them can quantitatively predict the variations. In one system, (Nb,Ti)3Sn, values of the normal-state resistivity just above the transition temperature were measured: adding 3 at. % Ti raises the value to ∼55 μΩ cm from the value of 10–15 μΩ cm for pure Nb3Sn. This increase in the resistivity is thought to be a primary reason for the increased Hc2 for this system as well as the other types of alloyed Nb3Sn which were studied here.

The effect of 3d-transition metal solutes on the ferrimagnetism of Fe 7Se 8

The effect of 3d-transition metal solutes on the magnetization of Fe 7Se 8 has been investigated by studying two series of alloys with constant solute concentrations of 3 and 10 at%, respectively. Small additions of Ti and V were sufficient to reduce the magnetization by one order of magnitude, whereas Ni slightly increased the magnetization. The changes due to the presence of Cr, Mn and Co were less noticeable. In certain cases the thermal treatment turned out to be a decisive factor in determining the type of magnetism. Alloys with Cr quenched from 1070 K were clearly antiferromagnetic. Quenched samples containing ten percent Ti were paramagnetic following a Curie-Weiss type law, but slow cooling from 1070 K reestablished the ferrimagnetic state. Order-disorder phenomena were assumed to be responsible for the changes due to the thermal treatment.

Influence of doping with titanium on the electronic structure of Ni3Fe and Ni3Mn in ordering

The specific electrical resistance ρ, mean magnetic moment μ of an atom of the alloy, and the anomalous Hall (Rs) and Nernst-Ettinghausen (Qs) constants of ordered alloys Ni3(Fe, Ti) and Ni3(Mn, Ti) are investigated. It is suggested that there is an additional degree of delocalization of the 3d electrons of the system Ni3(Mn, Ti) and increase in the degree of localization of 3d electrons of the system Ni3(Fe, Ti) with small additions of Ti, with increase in the long-range-order parameter. A model of the electronic structure of the given alloys is discussed.

Internal-Friction Study of Recrystallization in Pure Iron and Its Dilute Alloys

AbstractRecovery of high-temperature internal friction has been used as a means of studying recrystallization and lattice reorganization after cold working. Based on damping measurements at 1 Hz, this method is successful in detecting the solute effects produced by small additions of Ti, V, Co, and Ni (10–200 ppm (at.)) to pure iron (99.998%). The variation in activation-energy values for high-temperature internal friction of iron (10–29 kcal/g atom, 42–120 kJ/g atom) occurring under different conditions of cold working or annealing supports the hypothesis of a strict dependence of high-temperature internal friction on self-diffusion.

Boiling Mercury Corrosion of Certain Refractory Metals and Stainless Steels From 593–703C

Abstract Mercury corrosion of the refractory metals W, Mo, Ta and Cb-1Zr was studied in natural circulation quartz loops with two-phase mercury at temperatures from 593 to 703 C (1095–1295 F). Three thousand hour tests on these materials indicate that Ta and W showed no attack or weight loss and could not be detected in the mercury. Mo and Cb-1Zr alloy were detected in trace amounts in the mercury. Similar tests in quartz loops on Types 304 and 410 stainless steel also were completed. Effectiveness of small additions of Ti to the mercury in preventing corrosion was evaluated. Results indicate that Ti when added to mercury is effective in reducing mass transfer, of Type 410 stainless steel but appears to increase both the depth of corrosion and weight loss of Type 304.