Snoek-type damping performance in strong and ductile high-entropy alloys

Noise and mechanical vibrations not only cause damage to devices, but also present major public health hazards. High-damping alloys that eliminate noise and mechanical vibrations are therefore required. Yet, low operating temperatures and insufficient strength/ductility ratios in currently available high-damping alloys limit their applicability. Using the concept of high-entropy alloy (HEA), we present a class of high-damping materials. The design is based on refractory HEAs, solid-solutions doped with either 2.0 atomic % oxygen or nitrogen, (Ta0.5Nb0.5HfZrTi)98O2 and (Ta0.5Nb0.5HfZrTi)98N2. Via Snoek relaxation and ordered interstitial complexes mediated strain hardening, the damping capacity of these HEAs is as high as 0.030, and the damping peak reaches up to 800 K. The model HEAs also exhibit a high tensile yield strength of ~1400 MPa combined with a large ductility of ~20%. The high-temperature damping properties, together with superb mechanical properties make these HEAs attractive for applications where noise and vibrations must be reduced.

High-temperature damping capacity of fly ash cenosphere/AZ91D Mg alloy composites

In this study, fly ash cenospheres were added to semisolid AZ91D Mg alloy to prepare fly ash cenosphere/AZ91D (FAC/AZ91D) composites by means of compo-casting. The high-temperature damping capacity of FAC/AZ91D composites was investigated as compared with AZ91D Mg alloy. The results show that the damping capacities of FAC/AZ91D composites and AZ91D Mg alloy strongly depend on the measuring temperature. The FAC/AZ91D composites show better damping capacity than AZ91D Mg alloy. The 10 wt.% FAC/AZ91D composites exhibit the best damping capacity from room temperature to 125°C, whereas the 2 wt.% FAC/AZ91D composites show the highest damping capacity at 125°C–320°C. The damping mechanism was analyzed by microstructure observation at elevated temperatures. The damping-temperature curves exhibit a damping peak at approximately 150°C, and the activation energy of the damping peak was calculated according to the Arrhenius equation. Furthermore, the peak temperature increases with increasing frequencies. The damping peak is related to the thermal activation relaxation process, and its mechanism is the dislocation-induced damping.

Damping capacity of the Al matrix composite reinforced with SiC particle and TiNi fiber

Imitating the structure of steel-reinforced concrete, a composite coupling good damping capacity and mechanical property was fabricated by pressure infiltration progress. The aluminum (Al) matrix composite was hybrid reinforced by 20% volume fraction of SiC particle (SiCp) and 20% volume fraction of TiNi fiber (TiNif). The damping capacity of the composite in the temperature range from 30°C to 290°C was studied using a dynamic mechanical analyzer (DMA). Due to the B19′→B2 reverse martensitic transformation in TiNif, a damping peak showed up in the heating process. Furthermore, both the hysteretic effect of the martensite/variants interfaces in TiNif and the weak bonding interface between SiCp and TiNif were attributed to the high damping capacity of the composite. After tension deformation, a compressive stress was formed in the composite in the heating process. With the help of compressive stress, the value of the damping peak was much higher than before, since the movement of dislocation in the Al matrix was easier.

Mechanical and dynamic mechanical properties of polystyrene composites reinforced with cellulose fibers

The mechanical and dynamic mechanical properties of cellulose fibers-reinforced polystyrene composites were investigated as a function of cellulose fiber content and coupling agent effect. The composites were prepared using a corotating twin-screw extruder and after injection molding. Three levels of filler loading (10, 20, and 30 wt%) and a fixed amount of coupling agent (2 wt%) were used. The results showed that a cellulose fiber loading of more than 20 wt% caused decrease in the mechanical properties. The addition of coupling agent substantially improves the mechanical and dynamic mechanical properties. The use of coupling agent improved the storage modulus and reduced the damping peak values of the composites due to the improved interfacial adhesion. The height of the damping peak was found to be dependent on the content of cellulose fiber and the interfacial adhesion between fiber and matrix. The adhesion factor values confirm that the better adhesion occurs when coupling agent is used.

Effect of Annealing Temperature on Microstructure and Damping Capacity of Twin Roll Cast ZK60 Alloy

ZK60 alloy strip with 3.5mm thickness which produced by Twin Roll Casting (designated as TRC in short) was used in this paper. The effect of sequential annealing on microstructure and damping capacity of TRC ZK60 alloy was studied by using optical microscope (OM) and dynamic mechanical analyzer (DMA). The dendrite structure was present in TRC ZK60 alloy strip before and after annealing heat treatment. A few of recrystallized grains were present after annealed at 400°C for 1hr. The damping capacity of the strip as annealed at 400°C was better than that of annealed at the lower temperature. The room temperature (25°C) damping values (Q-1) of ZK60 strip which was annealed at 300°C, 350°C and 400°C were 0.0079, 0.0085 and 0.0096, respectively. The damping peak P1 is a relaxation process, but the damping peak P2 is not a relaxation process. The activation energy H for P1 of TRC ZK60 strip after annealed at 400°C for 1hr was 114KJ/mol. The damping peak P1 was attributed to boundary slip controlled by grain boundary diffusion and lattice self-diffusion.

Microstructures and Damping Capacity of Mg-6Zn-0.5Zr Alloy

The dynamic mechanical analyzer (DMA) was applied to investigate the damping properties of Mg-6Zn-0.6Zr alloys. The results show that the as-cast Mg-6Zn-0.6Zr alloy exhibits higher strain amplitude independent damping performance than that of as-homogenized. The strain amplitude dependent damping of the as-homogenized has the best damping performance with the strain amplitude from 3×10-5 to 6×10-4, and the as-extruded is the lowest. When the strain amplitude exceeded 6×10-4, the as-extruded has the best damping capacity all the time within the experimental strain amplitude, and all the alloys reach the high damping capacity. Two critical strain amplitude points were detected in the alloy as-extruded and as-homogenized. The damping peak value is 0.0192 with the strain amplitude of 1.5×10-3 presented in the alloy as-extruded.

Effects of Alloying Elements on the Oxygen Snoek-Type Relaxation in Ti-Nb Alloys

The effect of ternary alloying elements on the oxygen Snoek-type relaxation in the Ti-24Nb-2X-1.7O alloys (X = Al, Sn, Cr, Mn, Fe) was investigated. The dipole shape factor (δλ) of the Snoek-type relaxation was figured out for each ternary alloy based on the measured damping peak with the variable temperature. The value ofδλin the Ti-Nb-Al alloy was the highest among the present ternary alloys. It was found thatδλincreased with the decreasing lattice constant as well as the decreasing valence electron number per atom (e/a) and came to a maximum value when the e/a value was around 4.24, which defined the β phase boundary. Therefore, decreasing the lattice constants and the e/a value as largely as possible with alloying elements in the β-Ti alloys is one of the feasible ways to increaseδλand to design the high damping Ti alloys.

Effects of Phenolic Oligomer on the Dynamic Mechanical Properties of Nitrile Butadiene Rubber

In this article, the damping mechanism of organic hybrids consisting of Nitrile Butadiene Rubber (NBR) and phenolic oligomer 4-methyl-pheno reaction products of both dicyclopentadiene and isobutylene (MPDI) were investigated by dynamic mechanical analysis (DMA). It was shown that NBR/MPDI blends exhibit only one damping peak, which shifted to higher temperature with the increase of MPDI content, and the maximum of tan δ peak decreased slightly when the ratio of NBR/MPDI was no more than 100/20, and then increased when the ratio rised from 100/20 to 100/80. Fourier transform infrared spectrum (FT-IR) showed that the hydrogen bond were formed between -OH of MPDI and a-H of NBR. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements indicated that MPDI exhibit amorphous features, which was compatible with the blends. These may imply that much more stable damping material with both higher tan δ peak and controllable damping peak position can be achieved.

Effect of Zr Content on Properties of Mg-Zr PM Damping Alloys

Mg-xZr damping alloys (x=0.6, 1.5, 2.5, 5, mass %) were prepared by PM (powder metallurgy ) technology, and effects of Zr contents on microstructure, mechanical properties and damping capacities of Mg-xZr damping alloys were researched by three-point bending test and DMA, etc. The results show that the microstructure become into strip-shaped morphology, more granular particles appear in the grain boundaries or inside grains, and the grains are more refined with the increase of Zr additions. Micro-hardness and bending strength of the Mg-xZr damping alloys increase with increasing addition of Zr, and reach the maximum value with Zr addition of 2.5%. The damping capacities of Mg-xZr alloys increase slowly with the temperature from 27°C to 100°C, and increase rapidly above 100°C. The damping peaks appear at temperature of 160°C. Mg-5％Zr alloy exhibits the highest damping capacity, and its tanf value reaches to 0.084. The temperature of the damping peak increases with increasing frequencies, showing the characteristic of relaxation damping.