Furan Functionalized Polyesters and Polyurethanes for Thermally Reversible Reactive Hotmelt Adhesives

New reactive hotmelt (RHM) adhesives based on thermally reversible Diels-Alder networks comprising multifunctional furan and maleimide prepolymers are described. The prepolymer mixture is easy to apply in the bulk from the melt and after application to the substrates, the adhesive undergoes polymerization at room temperature resulting in crosslinked bonds. Due to their thermoplastic nature and low melt viscosity at hot melt application temperatures, the adhesives provide processing properties similar to moisture cured polyurethanes (PUR). The technology is isocyanate-free and does not require moisture to initiate the crosslinking. Bonding and tensile properties of the RHM adhesive can be readily tuned by prepolymer design and provide cure rates similar to PUR adhesives. The Diels-Alder adhesives provide versatile adhesion to a variety of substrates and good creep resistance up to the retro temperature. The adhesives show good thermal stability during application and can be recycled multiple times by simple heating/cooling of the bonds providing similar performance. Several furan and maleimide prepolymers were scaled up to multi-Kg quantities to demonstrate the potential for industrial scalability. The results demonstrate that furan-maleimide reversible chemistry can be used for RHM application as a more sustainable alternative to conventional moisture curing PURs which tend to contain harmful residual isocyanate monomers.

Study of Creep Test on Austenitic Stainless Steel

Study of creep properties of AISI 316 LN stainless steel has been carried out. AISI 316 LN is a contender material for major structural components for high temperature applications in boilers and heat exchangers due to its good mechanical properties at high temperatures, corrosion resistant with chemicals and adequate welding characteristics. The main aim of this research is to obtain creep data and study the compatibility of AISI 316 LN stainless steel for ultra-super critical (USC) boiler and heat exchanger applications. The creep test is carried out at 600°C and 700°C for constant applied loads below the yield strength. Study result obtained, time to undergo creep deformation for the applied parameters are more for AISI 316 LN compared to AISI 316 L. It is concluded that AISI 316 LN has good creep resistance than AISI 316 L.

Reinforcement of magnesium Elektron 21 with aluminium nitride (AlN) nanoparticles dispersed using a travelling magnetic field

Magnesium alloy Elektron 21 is commonly used in aerospace structural parts in which good creep resistance and lightness are required. This alloy maintains good mechanical properties at temperatures as high as 200 °C. One mechanism with high potential for improving mechanical properties of magnesium alloys at a high temperature is dispersion-strengthening based on nanoparticles. In this paper, we analyse the properties of magnesium Elektron 21 samples solidified with nanoparticles of aluminium nitride dispersed by an electromagnetic stirring provided from a travelling magnetic field. X-ray tomography and X-ray spectrometry as well as compression tests at several temperatures (350, 400 and 450 °C) are carried out on samples containing the nanoparticles. The present study extends the knowledge on the processing by alternative techniques and on the enhancement of creep behaviour at higher temperatures for such metal matrix composites compared to previous studies.

Multi objective Optimization of Turning Process Parameters at Different Conditions of Coolant Flow Rate

AA6064 is the most used nickel based super alloy. It is having high material strength, hardness and resistance to corrosion with good creep resistance. These properties in AA6064 is an attractive material and it is most commonly used in aerospace, gas turbine, marine and oil industries In this project machining of AA6064 is considered for the study. In these works three factors, cutting Speed (N), DOC (d), feed rate (f) are considered as parameters and their effect on metal removal rate (MRR) and surface roughness (SR) is studied through experimental investigation. The search for the optimal limited number of experimental runs, Taguchi’s orthogonal array L9 is used. In this three factors with three levels are considered to conduct the experiments and these experiments are conducted with three different conditions of coolant. Totally 27 experiments are conducted. Grey relational analysis employed to identify optimal combinational of process parameter values that minimize the surface roughness and maximize the metal removal rate..

The Influence of Laser Nitriding on Creep Behavior of Ti-4Al-4V Alloy with Widmanstätten Microstructure

Ti-6Al-4V alloy has been considered in applications of aeronautical and aerospace industries, due to its properties such as high specific resistance, good creep resistance and metallurgical stability. However, its use in applications for high temperatures is restricted due to its great affinity with the oxygen, which results in the formation of oxide layers and limits its mechanical resistance at these conditions. Thus, specific treatments have been employed in the material to work as surface barriers to avoid the oxygen diffusion in the alloy under high temperature conditions. One surface treatment that can be used is laser nitriding. In the present work, the surface of Ti-6Al-4V alloy with Widmanstätten microstructure was nitrided by applying Nd:YAG laser focal with 0.6 mm diameter, at laser power of 700, 750 and 800 W, process speed of 100 mm/s and 20 L/min of N2 flow. Creep tests were performed at constant load at 600 °C and 125 MPa, to verify the influence of treatment on the Ti-6Al-4V alloy. Results have indicated a lower stationary creep rate for the titanium alloy with Widmanstätten laser-nitrided structure when compared to the non-nitriding material. Besides that, the surface hardness increased from 368 HV of base material to 1000 HV after laser nitriding.

Preparation and Characterization of Pressureless Sintered Alumina/5 vol % SiC Micro-Nanocomposites

Alumina/5 vol % SiC micro-nanocomposites were produced by slip-casting and pressureless sintering. The dispersion of alumina and SiC particles in water using an electrosteric dispersant was studied for different solid contents. Although the rheological and granulometry measurements showed that the optimum amount of Darvan C for well-dispersing 50 wt % dry matter slurries was 0.20 vol %, this content was increased to 1.00 vol % in order to avoid the demixing of SiC nanoparticles during shaping. Well densified (>99%) alumina–SiC pressureless sintered materials were obtained at 1800 °C-2 h in which SiC nanoparticles occupied inter/intragranular positions. The creep behaviour of these materials was examined at 1200 °C under stresses ranging from 70 to 140 MPa. A good creep resistance in alumina-SiC materials was obtained demonstrating that the use of less expensive conventional sintering methods is possible and highlighting the importance of the dispersion step.

Research on High Temperature Creep Properties of Al2O3-SiO2 Ore (Al2O3 ~ 65)

High temperature creep properties of Al2O3-SiO2 ore (65% Al2O3 by mass percentage, abbreviation for Al2O3~65) was studied. The results show that the creep rates at 1300 °C × 50h, 1400 °C × 50h and 1500 °C × 50h were-0.89% ,- 1.75%, - 5.76%,respectively. At 1300 °C, ore has good creep resistance. As the temperature increases, the high temperature creep resistance of Al2O3 ~ 65 bauxite ore is significantly reduced. Creep process can be divided into two stages: when the time t <30h, the sample are in the densification process; after 30 hours, the creep properties show that the relationship between time and the creep rate is linear. At 1300 °C, the absolute value which is the slope of the linear relationship is smaller, exhibited an excellent high-temperature creep resistance. The loading softening-temperature of Al2O3 ~ 65 bauxite ore is 1343 °C. The Sample phase and microstructure are characterized by X-ray diffraction and scanning electron microscopy (SEM). The results show that mullite reticular is formed in sample at 1300 °C; at this point, TiO2 mostly exist as Rutile. At 1400 °C and 1500 °C, TiO2 mostly exist as Aluminum titanate, Corundum phase portion into mullite.

Deformation Mechanisms of Tandem Hot Rolled GH4169 Superalloy during Creep

By means of direct aged treatment, creep property measurement and high resolution TEM microstructure observation, the deformation mechanisms of Tandem Hot Rolled GH4169 superalloy during creep are investigated. Results show that, after direct aging treatment, fine γ″ particles with different sizes and shapes dispersedly precipitate in the alloy, which is one of important factors for the alloy possessing good creep resistance. And the deformation mechanisms of the alloy are that the deformed twinnings with different orientations are activated on {111} plane by pole mechanism, thereinto, the twinning dislocation may continuously slip around a pole axis dislocation on the twinning planes when the applied stress exceeds the critical value, and the twinnings may multiply by the dislocation reactions and mutual indemnification. As creep goes on, the denser dislocations with single or double orientations slip in the different twinnings, which play an important role of coordinating the grain deformation to enhance the creep resistance of the alloy.

Investigation on the Microstructures and Creep Properties of Mg-7~11wt. %Zn-4 wt. %Al Based Alloys

Recent studies indicated that Mg-(7-11)Zn-4Al (the composition of the alloys in the present paper are given in weight percentage.) based alloys exhibited good creep resistance and additions of trace alkaline elements to the alloys further improved the mechanical properties at elevated temperatures. In order to optimize the zinc concentration and reveal the effect of small amount of alkaline element additions to Mg-Zn-Al ternary alloys on their microstructure and elevated temperature creep resistance, five alloys with compositions of Mg-7Zn-4Al, Mg-9Zn-4Al, Mg-11Zn-4Al, Mg-11Zn-4Al-0.2Ca and Mg-11Zn-4Al-0.6Ca, respectively, were prepared in the present investigation and the microstructure and creep properties of these alloys were studied.

Synthesis and Sintering of Mullite Ceramics Using Microwave Heating

Mullite ceramics have been known as the engineering materials due to their special properties such as high refractoriness, good thermal shock resistance, low thermal expansion, good strength at low and high temperatures, good creep resistance and low dielectric constant. In the present work, mullite samples were prepared by reaction sinteing of alumina and silica gel and subsequent sintering in a microwave process. The sintering of samples was carried out at temperatures in the range of 1400-1500°C with no soaking time. Density and porosity measurements showed a high density (89.3% TD) and low porosity (5.8%) for samples sintered at 1400°C under microwave conditions while for samples sintered conventionally at this temperature after 2h heating, density decreased (81.9% TD) and porosity increased (18.5%). By increasing sintering temperature to 1450 and 1500°C under microwave conditions, density increased (93.3 and 93.8% TD) and porosity decreased (0.31 and 0.36%), respectively. Microhardness measurements showed 27.6% increment when sintering temperature increased from 1400 to 1500°C. The mean grain size increased (34.8%) for samples sintered in furnace rather than those sintered in microwave process.