Effects of Oxygen and Nitrogen Addition on Phase Transformation in Ti-10at%V

The addition of oxygen or nitrogen in titanium alloys increases the hardness by the solid solution strengthening. Spinodal decomposition in titanium alloys is also the way to increase the hardness. This study aimed to reveal the effect of oxygen or nitrogen addition on spinodal decomposition in Ti-10at%V. Ti-10at%V-(0, 1, 3)at%O or N alloys were prepared by arc-melting. They were solution-treated at 1200 or 1300 °C for 0.6 ks and then quenched in iced brine. The solution treated specimens were aged at 375 °C. The increase of hardness was decreased by the oxygen or nitrogen addition in the alloys. The addition of nitrogen more suppressed the age-hardening than the case of oxygen addition. The modulated structure caused by spinodal decomposition in the laths was observed in all the aged specimens. The wavelength of spinodal decomposition of the aged specimens increased with the addition of oxygen or nitrogen, leading to a decrease in age-hardening by spinodal decomposition.

Effect of Silicide on Dynamic Recrystallization in Near Alpha Titanium Alloy

Dynamic recrystallization in Ti-1100 was investigated. Ti-1100 is one of near α titanium alloys and contains Si for improving high temperature mechanical properties. Ti-1100 exhibits martensitic transformation by quenching into iced brine after solid solution treatment. Hereafter specimens subjected to quenching into iced brine and to cooling in air after solid solution treatment are called IBQ specimen and AC specimen, respectively. After tensile test at high temperature, IBQ specimen exhibits morphological change from lath structure to equiaxed structure, but AC specimen does not. It is indicated that dynamic recrystallization occurs during the tensile test of IBQ specimen. Effect of silicide on the dynamic recrystallization was investigated using two specimens: one included more silicide precipitates and the other less. The former specimen shows smaller recrystallized grains than the latter. It is indicated that the specimen including more silicides exhibits smaller recrystallized grains.

Effect of Quenching and Reheating on Isothermal Phase Transformation in Ti-15Nb-10Zr Alloy

Isothermal phase transformation in Ti-15Nb-10Zr (at%) alloys has been examined by mainly means of transmission electron microscopy. Specimens solution-treated at 1000°C in  phase field were directly held at temperatures between 350 and 450°C for 1.8-86.4ks, which are called "DH (direct holding)-specimen". On the other hand, some specimens solution-treated at 1000°C were quenched into iced brine and then aged at temperatures between 350 and 450°C, which are called "QA(quench and aging)-specimen". In the DH-specimen held at 400°C α phase formed in β matrix. Microstructure evolution of QA-specimen aged at 400°C, on the other hand, is as follows.  phase formed in β matrix after aging for 1.8ks and further aging led to growth of  phase. After prolonged aging, α phase started to form in β matrix. These experimental results indicate that process of the quenching and reheating promotes the formation of  phase. Specimen quenched into iced brine after solution treatment exhibited α'' phase formation. The α'' phase in the quenched specimen would transform into β phase during reheating to the aging temperature. Reversion process of α''  β phase could promote the formation of  phase in β. Microstructure formation in the DH- and QA-specimens at 350 and 450°C will also be explained.

Beta Phase Decomposition in a TiAl Alloy during Continuous Cooling

Beta phase decomposition in Ti-44Al-4Nb-4Hf-0.1Si during continuous cooling from β phase field has been investigated. A wide cooling rate range (0.3-1000°Cs-1) was provided by mainly using Jominy end quenching, which has been introduced into TiAl research recently, together with iced brine quench (IBQ) and furnace cooling (FC). At different cooling rates beta phase decomposes via different paths through diffusion or diffusionless mechanisms and lamellar transformation may occur after β decomposition at certain cooling rates.

Solidification Behavior of a 319 Aluminum Alloy

319 aluminum (6.5-8.5% Si, 3.0-4.0%Cu, 0.2-0.45%Mg, 0.8%max.Fe, 0.5%max.Mn) is utilized by the automobile industry for engine block and cylinder head applications. Detailed understanding of the solidification behavior is critical to optimizing the “as-cast” microstructure and the physical properties of this alloy. Samples were generated by allowing a 50 gram sample of molten alloy to partially solidify at a slow cooling rate (0.34 °C/sec). During cooling, the temperature of the alloy was monitored by a thermocouple in the center of the sample to generate a cooling curve (Fig. 1). At various locations along this cooling curve the normal cooling was interrupted by plunging the cup into an iced- brine quench. In addition to optical and SEM examination, detailed TEM analysis was performed on three quenched samples as well as one sample allowed to cool uninterrupted to room temperature. TEM sample preparation consisted of standard grinding and dimpling procedures followed by ion milling at liquid nitrogen temperature using a gun voltage of 4keV.

Diffraction study on bainite of Cu-Al alloy

Structure of bainite in Cu-Al and Cu-Zn-Al alloys has been reported as 3R, 9R or 18R long period stacking structure (LPS) by X-ray and electron diffraction studies. In the present work, a Cu-25.5 (at)% Al alloy sample was heated at 900°C for 2 h then isothermally held at 450°C for 60 s before quenching into iced brine. FIG.1 shows a TEM bright field image of bainite plates (marked B) grown from grain boundary. The parent phase ( with DO3 structure ) has transformed to martensite (marked M ) during cooling from 450° C to 0°C. Both bainite and martensite plates have dense striations inside.Careful diffraction study on a JEOL 2000FX TEM with accelerating voltage 200 KV revealed (FIG.2) that the diffraction patterns contai_ning the same zone axis [001] ( hexagonal index ) or [111]c ( cubic index ) are from a bainite plate with obtuse V-shape. They are indexed as [010], [140], [130], [120], [230], [340] and [110] zone pattern for hexagonal system respectively.

TEM Observations of Vanadium Carbide Reversion in an HSLA Steel

Microalloy precipitates in HSLA steels have relatively high equilibrium solubility temperatures. Being equilibrium phases, they are not normally associated with precipitate reversion processes. However, a recent observation has indicated that VC precipitate reversion may occur when HSLA steels are subjected to rapid heat treatment cycles. This investigation sought to determine if VC reversion occurs during rapid austenitization heat treatment cycles applied to a.14 wt% C,.48 wt% Mn and.49 wt% V HSLA steel.As-hot-rolled strips of the alloy were cut into sections VL cm by ∼0.5 cm thick. The equilibrium solubility temperature of VC in this alloy is 1037° C. Samples were initially solution treated at 1150°C for 1/2 hour, then quenched in iced brine solution to produce low carbon martensite.

Influence of Heat Treatments on Microstructures in an Fe-Co-V Alloy

The microstructural changes in an Fe-Co-V alloy (composition by wt.%: 2.97 V, 48.70 Co, 47.34 Fe and balance impurities, such as C, P and Ni) resulting from different heat treatments have been evaluated by optical metallography and transmission electron microscopy. Results indicate that, on air cooling or quenching into iced-brine from the high temperature single phase ϒ (fcc) field, vanadium can be retained in a supersaturated solid solution (α2) which has bcc structure. For the range of cooling rates employed, a portion of the material appears to undergo the γ-α2 transformation massively and the remainder martensitically. Figure 1 shows dislocation topology in a region that may have transformed martensitically. Dislocations are homogeneously distributed throughout the matrix, and there is no evidence for cell formation. The majority of the dislocations project along the projections of <111> vectors onto the (111) plane, implying that they are predominantly of screw character.

Martensite Transformation in β-NiAl

We present in this report some results of a study of the martensite transformation in the Ni-rich β-NiAl alloys. This transformation, first reported by Maxwell and Garla, has since been confirmed by several recent studies. Samples for the present study were prepared by vacuum-induction melting of the high purity elements with a nominal Al-68%Ni composition. Under equilibrium conditions, this alloy consists of single β-phase above 1350°C and a two-phase mixture of β and Ni3Al below this temperature. Martensitic transformation was introduced by quenching small rectangular-shaped samples in iced brine from above 1350°C, following equilibration in the β-range. The quenched samples were appreciably harder than the slow-cooled samples (770 vs. 390 VHN) and showed the typical acicular surface microstructure, shear markings within the grains, and often sharp steps at the grain boundaries, thus giving them a jagged appearance.

Dislocation Loops in Zn-0.7% Al Alloy

Dislocation loops have been reported mostly in fee metals and alloys after quenching from elevated temperatures and subsequent aging. This paper reports the formation and characteristics of dislocation loops in the hep Zn-0.7% Al alloy resulting from quenching and aging.Zn-0.7% Al sheet specimens, 0.001 inch thick, were quenched from temperatures of 275° to 375°C into iced brine. The aging temperature was -17°C or room temperature. Foil specimens were prepared by electropolishing and examined in a JEM-7 electron microscope.