Polymer-derived Ceramics as Innovative Oxidation Barrier Coatings for Mo-Si-B Alloys

2015 ◽  
Vol 1760 ◽  
Author(s):  
Manja Krüger ◽  
Georg Hasemann ◽  
Torben Baumann ◽  
Sebastian Dieck ◽  
Stefan Rannabauer
Keyword(s):  
Mechanical Properties ◽  
Elevated Temperatures ◽  
Silicon Oxide ◽  
Volume Fraction ◽  
Protective Coatings ◽  
High Volume ◽  
Dip Coating ◽  
Solid Solution Phase ◽  
Polymer Derived Ceramics ◽  
Three Phase

ABSTRACTThree phase Mo-Mo3Si-Mo5SiB2 alloys possess excellent mechanical properties over a wide temperature range. The Mo solid solution phase is needed for balanced mechanical properties at room temperature. However, this phase suffers from catastrophic oxidation behavior at high temperatures caused by the formation and evaporation of MoO3. The oxidation resistance of three phase alloys benefits from a high volume fraction of intermetallic phases. In particular Mo5SiB2 leads to the formation of a borosilicate protective glassy layer on the material’s surface while exposed to air at elevated temperatures. Hence, it is unlikely to identify alloy compositions that will yield both optimum mechanical and oxidation performance.Different coating systems and techniques, such as pack cementation, magnetron sputtering and plasma spraying are discussed in the literature to control the oxidation properties of Mo-based alloys. A different approach is to apply coating systems based on polymer derived ceramics (PDCs). Our present work introduces PDCs as a new type of promising and innovative oxidation-protective coatings for high temperature Mo-based alloys. After dip-coating with perhydropolysilazane (PHPS) and pyrolysis at 800 °C, dense and well-adhered SiNO ceramic layers could be achieved. These were investigated by scanning electron microscopy. Cyclic oxidation tests at 800 °C and 1100 °C were performed to investigate mass changes due to the thermal treatment. Indeed, even thin pyrolyzed PHPS layers with a thickness of around 70 nm to 175 nm protected the Mo-Si-B substrate during the initial stage of oxidation. By increasing the silicon oxide concentration at the material’s surface a first oxidation barrier was provided and thus, the strong initial mass loss could be decreased as compared to uncoated alloys. Furthermore, first results of the ongoing optimization process on PDC-coatings applied to Mo-Si-B alloys will be presented, involving the enhancement of the coating´s thickness or varying pyrolysis atmospheres.

Hot-die Forging of a β-stabilized γ-TiAl Based Alloy

2008 ◽  
Vol 1128 ◽  
Author(s):  
Wilfried Wallgram ◽  
Helmut Clemens ◽  
Sascha Kremmer ◽  
Andreas Otto ◽  
Volker Güther
Keyword(s):  
Mechanical Properties ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Small Deformation ◽  
High Volume ◽  
Compression Tests ◽  
Tial Alloys ◽  
Β Phase ◽  
Heat Treated ◽  
Hot Die Forging

AbstractBecause of the small “deformation window” hot-working of γ-TiAl alloys is a complex and difficult task and, therefore, isothermal forming processes are favoured. In order to increase the deformation window a novel Nb and Mo containing γ-TiAl based alloy (TNM™ alloy) was developed. Due to a high volume fraction of β-phase at elevated temperatures the alloy can be hot-die forged under near conventional conditions, which means that conventional forging equipment with minor and inexpensive modifications can be used. With subsequent heattreatments balanced mechanical properties can be achieved. This paper summarizes our progress in establishing a “near conventional” forging route for the fabrication of γ-TiAl components. The results of lab scale compression tests and forging trials on an industrial scale are included. In addition, the mechanical properties of forged and heat-treated TNM™ material are presented.

scholarly journals Effect of Elevated Temperature on Mechanical Properties of High-Volume Fly Ash-Based Geopolymer Concrete, Mortar and Paste Cured at Room Temperature

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1473
Author(s):  
Jun Zhao ◽  
Kang Wang ◽  
Shuaibin Wang ◽  
Zike Wang ◽  
Zhaohui Yang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Elevated Temperature ◽  
Fly Ash ◽  
Residual Strength ◽  
Elevated Temperatures ◽  
High Volume ◽  
Sem Analysis ◽  
Geopolymer Concrete ◽  
Ordinary Concrete ◽  
Exposure Temperature

This paper presents results from experimental work on mechanical properties of geopolymer concrete, mortar and paste prepared using fly ash and blended slag. Compressive strength, splitting tensile strength and flexural strength tests were conducted on large sets of geopolymer and ordinary concrete, mortar and paste after exposure to elevated temperatures. From Thermogravimetric analyzer (TGA), X-ray diffraction (XRD), Scanning electron microscope (SEM) test results, the geopolymer exhibits excellent resistance to elevated temperature. Compressive strengths of C30, C40 and C50 geopolymer concrete, mortar and paste show incremental improvement then followed by a gradual reduction, and finally reach a relatively consistent value with an increase in exposure temperature. The higher slag content in the geopolymer reduces residual strength and the lower exposure temperature corresponding to peak residual strength. Resistance to elevated temperature of C40 geopolymer concrete, mortar and paste is better than that of ordinary concrete, mortar and paste at the same grade. XRD, TGA and SEM analysis suggests that the heat resistance of C–S–H produced using slag is lower than that of sulphoaluminate gel (quartz and mullite, etc.) produced using fly ash. This facilitates degradation of C30, C40 and C50 geopolymer after exposure to elevated temperatures.

MICROSTRUCTURE AND MECHANICAL BEHAVIOR OF AMORPHOUS Al–Cu–Ti METAL FOAMS SYNTHESIZED BY SPARK PLASMA SINTERING

2017 ◽  
Vol 24 (Supp02) ◽  
pp. 1850022
Author(s):  
MAOYUAN LI ◽  
LIN LU ◽  
ZHEN DAI ◽  
YIQIANG HONG ◽  
WEIWEI CHEN ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Intermetallic Compounds ◽  
Spark Plasma Sintering ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Metal Foams ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Xrd Patterns

Amorphous Al–Cu–Ti metal foams were prepared by spark plasma sintering (SPS) process with the diameter of 10[Formula: see text]mm. The SPS process was conducted at the pressure of 200 and 300[Formula: see text]MPa with the temperature of 653–723[Formula: see text]K, respectively. NaCl was used as the space-holder, forming almost separated pores with the porosity of 65 vol%. The microstructure and mechanical behavior of the amorphous Al–Cu–Ti metal foams were systematically investigated. The results show that the crystallinity increased at elevated temperatures. The effect of pressure and holding time on the crystallization was almost negligible. The intermetallic compounds, i.e. Al–Ti, Al–Cu and Al–Cu–Ti were identified from X-ray diffraction (XRD) patterns. It was found that weak adhesion and brittle intermetallic compounds reduced the mechanical properties, while lower volume fraction and smaller size of NaCl powders improved the mechanical properties.

scholarly journals The Effect of Stepped Austempering on Phase Composition and Mechanical Properties of Nanostructured X37CrMoV5-1 Steel

2015 ◽  
Vol 60 (1) ◽  
pp. 517-521
Author(s):  
S. Marciniak ◽  
E. Skołek ◽  
W. Świątnicki
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Isothermal Annealing ◽  
Volume Fraction ◽  
Bainitic Ferrite ◽  
High Volume ◽  
Thin Layers ◽  
Strength Parameters ◽  
One Step ◽  
Step Heat Treatment

AbstractThis paper presents the results of studies of X37CrMoV5-1 steel subjected to quenching processes with a one-step and a two-step isothermal annealing. The TEM observation revealed that steel after one-step treatment led is composed of carbide-free bainite with nanometric thickness of ferrite plates and of high volume fraction of retained austenite in form of thin layers or large blocks. In order to improve the strength parameters an attempt was made to reduce the austenite content by use of quenching with the two-step isothermal annealing. The temperature and time of each step were designed on the basis of dilatometric measurements. It was shown, that the two-step heat treatment led to increase of the bainitic ferrite content and resulted in improvement of steel's strength with no loss of steel ductility.

Microstructures and Mechanical Properties of 6061 Al Matrix Smart Composite Containing TiNi Shape Memory Fiber

1996 ◽  
Vol 459 ◽  
Author(s):  
J. H. Lee ◽  
K. Hamada ◽  
K. Miziuuchia ◽  
M. Taya ◽  
K. Inoue
Keyword(s):  
Mechanical Properties ◽  
Shape Memory ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Matrix Material ◽  
Matrix Alloy ◽  
Flow Strength ◽  
The Matrix ◽  
Shape Memory Fiber ◽  
Al Matrix

ABSTRACT6061 Al-matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by vacuum hot pressing to investigate the microstructure and mechanical properties. The yield stress of this composite increases with increasing amount of prestrain, and it also depends on the volume fraction of fiber and heat treatment. The smartness of the composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stresses in the matrix material when heated after being prestrained. Microstructual observations have revealed that interfacial reactions occur between the matrix and fiber, creating two intermetallic layers. The flow strength of the composite at elevated temperatures is significantly higher than that of the matrix alloy without TiNi fiber.

A MIM Route for Producing Ti6Al4V-TiC Composites

2016 ◽  
Vol 704 ◽  
pp. 139-147 ◽  
Author(s):  
Roger Pelletier ◽  
Louis Philippe Lefebvre ◽  
Eric Baril
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Wear Resistance ◽  
Elevated Temperatures ◽  
Metallic Matrix ◽  
High Volume ◽  
Metal Injection Molding ◽  
Titanium Matrix ◽  
Size Refinement ◽  
Specific Strength

Discontinuous reinforced titanium matrix composites have generated significant interest due to their compelling properties such as their specific strength and wear resistance at room and elevated temperatures. For these reasons, these materials have been considered in various applications such as automotive (valve components), aerospace (engine components) and medical devices (implants). Metal injection molding (MIM) has proven to be an efficient near net-shape technology suitable for high volume manufacturing of parts having complex geometries. The MIM technology is particularly attractive for producing composites as the metallic matrix does not go through the liquid state. This helps minimizing the segregation of the hard particles. MIM also reduces the needs for machining. However, the production of titanium components with the MIM process has its own challenges and limitations, such as presence of porosities and coarser microstructures compared to wrought products. The present work introduces the results obtained during the development of a MIM route for producing Ti6Al4V-5wt%TiC composites. The feedstock developed is wax-based and incorporates a pre-alloyed metal powder. The microstructure, mechanical properties at room and elevated temperatures, the wear resistance and the thermal diffusivity of the composites have been characterised. Properties are compared with those of a Ti6Al4V MIM material produced with the same feedstock and process but without TiC as well as with those of wrought Ti6Al4V reported in the literature. The presence of a small amount of TiC promotes densification and grain size refinement and affects the surface finish of the sintered components. Tensile properties of the composites are comparable or better than those of wrought Ti6Al4V (ASTM F1472). Improved mechanical properties compared to unreinforced material are associated to the higher density, finer grain size as well as solution strengthening of the titanium matrix.

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