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+49 3677 69-1841
Silke Stauche
Coordinator for Master Admissions
Max-Planck-Ring 12
Werner-Bischoff-Bau
+49 3677 69-1841
Authors: Mozhgan Gholami-Kermanshahi; Yuan-Chien Hsiao; Günther Lange; Shih-Hang Chan
In this study, we analyze the influences of carbon nanotube (CNT) addition on the martensite transformation and internal friction of Cu-Al-Ni shape-memory alloys (SMAs). X-ray diffraction and differential scanning calorimetry results demonstrate that Cu-13.5Al-4Ni-xCNT(x= 0, 0.2, 0.4, 0.6, and 0.8 wt%) SMA/CNT composites exhibit a β1(DO3)⇄ß'1(18R) martensitic transformation. The martensitic transformation temperatures and transformation enthalpies of the martensitic transformation peaks for the Cu-13.5Al-4Ni-xCNT(x= 0-0.8 wt%) composites gradually decrease with the increase in the amount of CNT addition. Compared to the Cu-13.5Al-4Ni SMA, the Cu-13.5Al-4Ni-xCNT(x = 0.2-0.8 wt%) SMA/CNT composites exhibit significant improvements in the amount of dissipation of energy (storage modulus (E′)) and mechanical strength. However, the tan δ of the internal friction peak gradually decreases with the increase in the CNT content above 0.6 wt%. The reduction in tan δ is attributed to the decrease in the magnitude of the austenite-to-martensite transformation and precipitation of γ2 (Cu9Al4) phase particles, which impede the interface motion in between the parent/martensitic phase and martensitic phase.
Authors: Mozhgan Gholami-Kermanshahi; Yu-Yan Wu; Günther Lange; Shih-Hang Chang
Abstract: This study investigates the damping properties of Cu-Al-Mn shape memory alloys (SMAs) with various chemical compositions and the effects of the addition of quaternary alloying elements Ag and Nb on the microstructure, martensitic transformation behavior, and damping capacity of SMAs. Compared to other Cu-12Al-xMn(x = 4-7 wt. %) SMAs, Cu-12Al-5Mn has a more significant inherent and intrinsic internal friction (IFPT + IFI) peak above room temperature. The addition of Ag or Nb to Cu-12Al-5Mn reduced the grain size, thereby increasing the hardness of the alloys; however, the damping capacity and temperature of the IFPT + IFI peak decreased simultaneously. The addition of Ag to Cu-12Al-5Mn significantly reduced the damping capacity (IFPT+IFI peak) because of the notable decrease in the amount of transformed martensite. Moreover, the addition of Nb to Cu-12Al-5Mn caused the AlNb3 phase to precipitate, limiting the mobility of the martensite variant interfaces and slightly decreasing the damping capacity (IFPT + IFI peak). Among the Ag- and Nb-doped Cu-12Al-5Mn SMAs, Cu-12Al-5Mn-1 Nb showed not only a significantly higher hardness but also a higher IFPT + IFI peak, with tan δ exceeding 0.01 at approximately 50 °C.
ScienceDirect: Journal of Alloys and Compounds; October 3, 2022
Fiber and Fiber-Surface Treatment Effects in Foamability of Carbon Fiber Reinforced Aluminum Alloy Composites Foam
Light materials have become very important in most manufacturing sectors such as aviation and transportation industries. Much research has been done to improve the mechanical properties of lightweight materials, especially lightweight, high-performance aluminum foam composite materials. The mechanical properties of carbon fiber reinforced aluminum foam have the potential to depend on wetting and bonding of carbon fiber in the aluminum matrix. This paper provides a systematic design and procedure for developing aluminum foam composites using carbon fiber as a reinforcement and AlMg4Si8 alloy as a matrix (AMFC-aluminum matrix foam composite) were produced by powder metallurgy. Nickel coating on the carbon fiber surface is applied to control the reactivity of the interface of the fiber with aluminum during the manufacture of the composite to improve wettability between carbon fiber and aluminum. The effects of chemical oxidation and nickel coating on carbon fiber in the wettability of carbon fiber in aluminum foam were confirmed scanning electron microscopic analysis. Digital images produced by the imaging system are used with the MATLAB algorithm to determine the surface porosity and pore areaof aluminum foam in an efficient manner. The results can have important implications for the processing of carbon fiber reinforced aluminum foam composites and their mechanical properties.
Chemical oxidation and electroless deposition nickel coating ofMWCNT (Multi-walled carbon nanotubes) have been carriedout to improve the distribution and the wettability of MWCNTin the aluminum foam. MWCNT reinforced AlMg4Si8 foam(AMFC-aluminum matrix foam composite) were produced bypowder metallurgy. The effects of chemical oxidation andnickel coating on MWCNT in the dispersion of MWCNT in thealuminum foam were confirmed by scanning electronmicroscopic analysis. Observation of the distribution of theMWCNT in the aluminum foam matrix showed that thetechnique is effective in dispersing and increase the wettabilityof the MWCNT coated nickel within the aluminum foam matrix.
