Alpha Case Characterization of Hot Rolled Titanium

2014 ◽  
Vol 1019 ◽  
pp. 311-317 ◽  
Author(s):  
Francois Conradie ◽  
Nico Treurnicht ◽  
Natasha Sacks
Keyword(s):  
Titanium Alloys ◽  
Oxide Layer ◽  
Fatigue Crack Initiation ◽  
Weight Ratio ◽  
Inert Gas ◽  
Atmospheric Conditions ◽  
Capital Costs ◽  
Alpha Case ◽  
Gas Atmosphere ◽  
Chemical Milling

Titanium alloys offer excellent corrosion resistance, good strength to weight ratio, is nonmagnetic and biocompatible. This allows them to be used in demanding applications and specialised industries ranging from aviation to medicine. However, at high temperatures the metal is chemically reactive which requires several manufacturing processes such as melting and welding to be performed either in vacuum or inert gas atmosphere. Some processes such as rolling are impractical to be performed in inert gas atmosphere. Titanium alloys, notably Ti-6Al-4V, develops a hard oxide layer on the outer surface during hot processing, such as rolling, in atmospheric conditions. This oxide layer, commonly referred to as the alpha case, is both hard and brittle. The increased Young's modulus of the alpha case creating an outer layer with increased stiffness where maximum stresses occur, results in localized micro failure. The micro failures in this layer serve as a fatigue crack initiation zone, compromising the integrity of the component and causing it to fail. Traditionally alpha case is removed by means of chemical milling in hot acid baths using aggressive acids such as Hydrofluoric acid. The facilities needed for chemical milling require high capital costs as well as stringent and costly safety requirements. Lastly, the disposal of used acids is proving to become increasingly difficult due to the strict South African environmental laws. Removal of this layer by means of light pass machining has therefore become more desirable, however at present it remains economically infeasible. This study presents an overview of the materials background, alpha case formation and related machining considerations. Experiments that investigate alpha case properties are included.

High Pressure Waterjets – An Innovative Means of Alpha Case Removal for Superplastically Formed Titanium Alloys

2010 ◽  
Vol 433 ◽  
pp. 103-111 ◽  
Author(s):  
A. Chillman ◽  
Mamidala Ramulu ◽  
M. Hashish ◽  
A. Cantrell
Keyword(s):  
High Pressure ◽  
Titanium Alloys ◽  
Material Removal ◽  
Work Piece ◽  
Fine Grain ◽  
Alpha Case ◽  
Material Erosion ◽  
Chemical Milling ◽  
Repetitive Impact ◽  
Cleaning Methods

Ultra high-pressure waterjets (WJ) have gained consideration as a viable alternative to conventional material removal and cleaning methods such as chemical milling, grit blasting, and grinding. Waterjets have often been considered for the stripping of unwanted coatings, but they also exhibit an inherent ability for the controlled milling of metallic materials. The waterjet material removal process poses a secondary benefit – the material erosion occurs due to the repetitive impact of droplets within the waterjet stream, which also serve to induce compressive residual stresses in the shallow sub-surface layers of the work piece. An experimental study was conducted to explore the removal of the alpha case layer on Superplastically Formed conventional and fine grain Ti-6Al-4V specimens. The resulting surface roughness parameters and completeness of alpha layer removal were characterized. Based on the experimental results, waterjet removal processes may serve as an alternate method for the post-processing of Superplastically Formed titanium alloys.

scholarly journals Influence of Manufacturing Conditions on Inclusion Characteristics and Mechanical Properties of FeCrNiMnCo Alloy

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1286
Author(s):  
Nuri Choi ◽  
Nokeun Park ◽  
Jin-kyung Kim ◽  
Andrey V. Karasev ◽  
Pär G. Jönsson ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Impurity Content ◽  
Inert Gas ◽  
Molten Alloy ◽  
Vacuum Induction Melting ◽  
Induction Melting ◽  
Atmospheric Conditions ◽  
Air Exposure ◽  
High Entropy ◽  
Gas Atmosphere

Three CoCrFeMnNi high-entropy alloys (HEAs) were produced by vacuum induction melting, induction melting under inert gas atmosphere, and melting under inert gas atmosphere followed by air exposure, respectively. The different manufacturing conditions for the three investigated alloys resulted in different levels and types of inclusions. The alloys melted under vacuum or inert gas contained Al2O3 inclusions formed by impurity Al, due to its high oxidation tendency. The molten alloy exposed in air showed an excessive oxidation. During oxidation of the molten alloy in air, impurity Al was initially oxidized, and fine MnCr2O4 inclusions were formed rather than pure Al2O3 inclusions. This difference was analyzed based on thermodynamic calculations. Specifically, the influence of impurity content on the inclusion characteristics was investigated for the three HEAs. Moreover, the inclusion characteristics were found to have an influence on mechanical properties of the alloys also. In air-exposed HEA, smaller inclusions were formed, resulting in a higher dislocation density at the matrix/inclusion interface and thus strengthening of the HEA. Thus, it is proposed that atmospheric conditions could be an important factor to control the inclusion characteristics and to form fine inclusion particles, which could improve the mechanical properties of HEAs.

Development and Removal of Alpha-Case Layer From Heat Treated Titanium Alloys

2017 ◽  
Author(s):  
Nikita Mohite ◽  
Sachin Biradar ◽  
Jyoti Shankar Jha ◽  
Sushil Mishra ◽  
Asim Tewari
Keyword(s):  
Oxide Layer ◽  
Elevated Temperatures ◽  
Fatigue Crack Initiation ◽  
Fixed Time ◽  
Hardness Profile ◽  
Air Cooling ◽  
Initiation Zone ◽  
Alpha Case ◽  
Heat Treated ◽  
Aero Engines

The components of the aero engines such as fan blades are generally manufactured from Titanium alloy forgings. At the elevated temperatures, the affinity of Titanium towards oxygen is very high, which results in formation of oxide layer on surface known as alpha-case layer. This alpha-case is both hard and brittle in nature which results in localized micro failure during its application. This gives rise to a fatigue crack initiation zone and compromises the integrity of the component, causing it to fail. To investigate this, Titanium α-β (Ti 64), α (Sn) and β (Mo) alloys were heat treated at 1010°C for 30min, 60min, 90min and 120min followed by air cooling. Formation of alpha-case layer in Ti-6Al-4V, Ti-Sn and Ti-Mo increased from 120.5μm to 391.1μm, 128.77μm to 443.23μm, 105.75μm to 262.46μm at 30mins and 120mins respectively. Chemical treatment, cathodic de-oxygenation, surface coating and laser ablation methods are generally used to remove the alpha case. In the current study, acid pickling is used to remove the alpha case layer, as this process is simple and also easily applicable to any complex shape of the material. In this method, samples were dipped in the solution of HF (5%) and HNO3 (35%) at 80 °C for fixed time at fixed intervals to find the rate of alpha case removal. Micro indentation was carried out to obtain hardness profile from surface to bulk of heat treated specimen. The quantification of alpha case oxide layer from surface to bulk was done by EDS.

Recent Progress In High-Resolution Shadowing For Biological Transmission Electron Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 510-511 ◽  
Author(s):  
Heinz Gross ◽  
Katarina Krusche ◽  
Peter Tittmann
Keyword(s):  
Heavy Metal ◽  
High Resolution ◽  
Freeze Drying ◽  
Atmospheric Conditions ◽  
Vacuum Equipment ◽  
Transmission Electron ◽  
Gas Atmosphere ◽  
Gas Molecules ◽  
Residual Gas ◽  
Backing Layer

Freeze-drying followed by heavy metal shadowing is a long established and straight forward approach to routinely study the structure of dehydrated macromolecules. Very thin specimens such as isolated membranes or single macromolecules are directly adsorbed on C-coated grids. After rapid freezing the grids are transferred into a suitable vacuum equipment for freeze-drying and heavy metal shadowing.To improve the resolution power of shadowing films we introduced shadowing at very low specimen temperature (−250°C). To routinely do that without the danger of contamination we developed in collaboration with Balzers an UHV (p≤10-9 mbar) machine (BAF500K, Fig.2). It should be mentioned here that at −250°C the specimen surface acts as effective cryopump for practically all impinging residual gas molecules from the residual gas atmosphere.Common high resolution shadowing films (Pt/C, Ta/W) have to be protected from alterations due to air contact by a relatively thick C-backing layer, when transferred via atmospheric conditions into the TEM. Such an additional C-coat contributes disturbingly to the contrast at high resolution.

scholarly journals Recovery of Hydrogen Isotopes by Pd-coated ZrNi from Inert Gas Atmosphere Containing Impurities

2001 ◽  
Vol 38 (11) ◽  
pp. 952-958 ◽  
Author(s):  
Kan ASHIDA ◽  
Yuji HATANO ◽  
Wataru NISHIDA ◽  
Kuniaki WATANABE ◽  
Asami AMANO ◽  
...  
Keyword(s):  
Hydrogen Isotopes ◽  
Inert Gas ◽  
Gas Atmosphere

WETTING BEHAVIOR IN ULTRASONIC VIBRATION-ASSISTED BRAZING OF ALUMINUM TO GRAPHITE USING Sn-Ag-Ti ACTIVE SOLDER

2015 ◽  
Vol 22 (03) ◽  
pp. 1550035 ◽  
Author(s):  
WEI-YUAN YU ◽  
SEN-HUI LIU ◽  
XIN-YA LIU ◽  
JIA-LIN SHAO ◽  
MIN-PEN LIU
Keyword(s):  
Oxide Layer ◽  
Ultrasonic Vibration ◽  
Pure Aluminum ◽  
Decomposition Temperature ◽  
Ultrasonic Waves ◽  
Atmospheric Conditions ◽  
Liquid Solder ◽  
Ambient Conditions ◽  
Composite Oxides ◽  
Surface Oxides

In this study, Sn - Ag - Ti ternary alloy has been used as the active solder to braze pure aluminum and graphite in atmospheric conditions using ultrasonic vibration as an aid. The authors studied the formation, composition and decomposition temperature of the surface oxides of the active solder under atmospheric conditions. In addition, the wettability of Sn -5 Ag -8 Ti active solder on the surface of pure aluminum and graphite has also been studied. The results showed that the major components presented in the surface oxides formed on the Sn -5 Ag -8 Ti active solder under ambient conditions are TiO , TiO 2, Ti 2 O 3, Ti 3 O 5 and SnO 2. Apart from AgO and Ag 2 O 2, which can be decomposed at the brazing temperature (773 K), other oxides will not be decomposed. The oxide layer comprises composite oxides and it forms a compact layer with a certain thickness to enclose the melted solder, which will prevent the liquid solder from wetting the base metals at the brazing temperature. After ultrasonic vibration, the oxide layer was destroyed and the liquid solder was able to wet and spread out around the base materials. Furthermore, better wettability of the active solder was observed on the surface of graphite and pure aluminum at the brazing temperature of 773–823 K using ultrasonic waves. The ultrasonic wave acts as the dominant driving factor which promotes the wetting and spreading of the liquid solder on the surface of graphite and aluminum to achieve a stable and reliable brazed joint.

Improvement of Surface Roughness in End Milling of Ti6Al4V by Coupling RSM with Genetic Algorithm

2011 ◽  
Vol 264-265 ◽  
pp. 1154-1159
Author(s):  
Anayet Ullah Patwari ◽  
A.K.M. Nurul Amin ◽  
S. Alam
Keyword(s):  
Genetic Algorithm ◽  
Surface Roughness ◽  
Titanium Alloys ◽  
End Milling ◽  
Fitness Function ◽  
Cutting Speed ◽  
Weight Ratio ◽  
Cutting Parameters ◽  
Depth Of Cut ◽  
Resistance Surface

Titanium alloys are being widely used in the aerospace, biomedical and automotive industries because of their good strength-to-weight ratio and superior corrosion resistance. Surface roughness is one of the most important requirements in machining of Titanium alloys. This paper describes mathematically the effect of cutting parameters on Surface roughness in end milling of Ti6Al4V. The mathematical model for the surface roughness has been developed in terms of cutting speed, feed rate, and axial depth of cut using design of experiments and the response surface methodology (RSM). Central composite design was employed in developing the surface roughness models in relation to primary cutting parameters. The experimental results indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors that are being investigated. The developed RSM is coupled as a fitness function with genetic algorithm to predict the optimum cutting conditions leading to the least surface roughness value. MATLAB 7.0 toolbox for GA is used to develop GA program. The predicted results are in good agreement with the experimental one and hence the model can be efficiently used to achieve the minimum surface roughness value.

scholarly journals Investigating green infrastructure as potential medium for ground heat exchangers

2020 ◽  
Vol 205 ◽  
pp. 06013
Author(s):  
Anil Yildiz ◽  
Ross A. Stirling
Keyword(s):  
Soil Temperature ◽  
Green Infrastructure ◽  
Heat Exchangers ◽  
Heat Dissipation ◽  
Power Input ◽  
Atmospheric Conditions ◽  
Heat Rejection ◽  
Capital Costs ◽  
Ground Heat Exchangers ◽  
Heating And Cooling

Space heating and cooling comprises a significant portion of the overall energy consumption. Ground heat exchangers (GHE), are a sustainable alternative to conventional, non-renewably powered heating and cooling systems. Space is a scarce resource in densely urbanised areas, allocating dedicated locations to build GHE systems can result in high initial capital costs and an inflexibility in retrofitting. An alternative solution is to utilise existing, multi-benefit and resilient Sustainable Drainage Systems (SuDS) in cities. An investigation into the feasibility of utilising SuDS as sites for potential GHEs requires an understanding of their thermal and hydrological behaviour and boundary conditions. This study utilises a heavily-instrumented, vegetated lysimeter setup, exposed to atmospheric conditions, to test a pilot-scale SuDS heat exchanger. Heat rejection into the substrate of a SuDS has been simulated with the application of heat via voltage-controlled heating cables at a depth of 850 mm for 72-hour durations (at three different power inputs) with 96-hours between each power input. These heat dissipation periods are reflected in measured soil temperature profiles. Volumetric water content, matric suction, soil temperature and heat flux are monitored at various locations in the lysimeter. A finite difference modelling scheme has been developed to simulate the variation in soil temperature due to heat rejection.

scholarly journals Electrochemical Anodizing Treatment to Enhance Localized Corrosion Resistance of Pure Titanium

2017 ◽  
Vol 15 (1) ◽  
pp. 19-24 ◽  
Author(s):  
Davide Prando ◽  
Andrea Brenna ◽  
Fabio M. Bolzoni ◽  
Maria V. Diamanti ◽  
Mariapia Pedeferri ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Titanium Alloys ◽  
Oxide Layer ◽  
Corrosion Behavior ◽  
Pure Titanium ◽  
Localized Corrosion ◽  
Anodic Current Density ◽  
Anodic Current ◽  
Protective Oxide ◽  
Pitting Potential

Background Titanium has outstanding corrosion resistance due to the thin protective oxide layer that is formed on its surface. Nevertheless, in harsh and severe environments, pure titanium may suffer localized corrosion. In those conditions, costly titanium alloys containing palladium, nickel and molybdenum are used. This purpose investigated how it is possible to control corrosion, at lower cost, by electrochemical surface treatment on pure titanium, increasing the thickness of the natural oxide layer. Methods Anodic oxidation was performed on titanium by immersion in H2SO4 solution and applying voltages ranging from 10 to 80 V. Different anodic current densities were considered. Potentiodynamic tests in chloride- and fluoride-containing solutions were carried out on anodized titanium to determine the pitting potential. Results All tested anodizing treatments increased corrosion resistance of pure titanium, but never reached the performance of titanium alloys. The best corrosion behavior was obtained on titanium anodized at voltages lower than 40 V at 20 mA/cm2. Conclusions Titanium samples anodized at low cell voltage were seen to give high corrosion resistance in chloride- and fluoride-containing solutions. Electrolyte bath and anodic current density have little effect on the corrosion behavior.

Characterization of nanomagnetites co-precipitated in inert gas atmosphere for plant nutrition

2018 ◽  
Vol 239 (1) ◽  
Author(s):  
A. Lengyel ◽  
Z. Homonnay ◽  
K. Kovács ◽  
Z. Klencsár ◽  
Sz. Németh ◽  
...  
Keyword(s):  
Plant Nutrition ◽  
Inert Gas ◽  
Gas Atmosphere
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