Thermomechanical Behavior of Low CTE Metal-Matrix Composites Fabricated Through Ultrasonic Additive Manufacturing

Shape memory and superelastic NiTi are often utilized for their large strain recovery and actuation properties. The objective of this research is to utilize the stresses generated by pre-strained NiTi as it is heated in order to tailor the CTE of metal-matrix composites. The composites studied consist of an Al 3003-H18 matrix with embedded NiTi ribbons fabricated through an emerging rapid prototyping process called Ultrasonic Additive Manufacturing (UAM). The thermally-induced strain of the composites is characterized and results show that the two key parameters in adjusting the effective CTE are the NiTi volume fraction and prestrain of the embedded NiTi. From the observed behavior, a constitutive composite model is developed based constitutive SMA models and strain matching composite models. Additional composites were fabricated to characterize the NiTi-Al interface through EDS and DSC. These methods were used to investigate the possibility of metallurgical bonding between the ribbon and matrix and determine interface shear strength. Interface investigation indicates that mechanical coupling is accomplished primarily through friction and the shear strength of the interface is 7.28 MPa. Finally, using the developed model, a composite was designed and fabricated to achieve a near zero CTE. The model suggests that the finished composite will have a zero CTE at a temperature of 135°C.