DOA Estimation Method Using Sparse Representation with Orthogonal Projection

In order to reduce the effect of noises on DOA estimation,this paper proposes a direc-tion-of-arrival(DOA)estimation method using sparse representation with orthogonal projection(OPSR).The OPSR method obtains a new covariance matrix by projecting the covariance matrix of the array data to the signal subspace,leading to the elimination of the noise subspace.After-wards,based on the new covariance matrix after the orthogonal projection,a new sparse representa-tion model is established and employed for DOA estimation.Simulation results demonstrate that compared to other methods,the OPSR method has higher angle resolution and better DOA estima-tion performance in the cases of few snapshots and low SNRs.

Microstructural Evolution and Mechanical Properties of Inconel 625 Alloy during Pulsed Plasma Arc Deposition Process

Pulsed plasma arc deposition （PPAD）, which combines pulsed plasma cladding with rapid prototyping, is a promising technology for manufacturing near net shape components due to its superiority in cost and convenience of processing. In the present research, PPAD was successfully used to fabricate the Ni-based superalloy Inconel 625 components. The microstructures and mechanical properties of deposits were investigated by scanning electron microscopy （SEM）, optical microscopy （OM）, transmission electron microscopy （TEM） with energy dispersive spectrometer （EDS）, microhardness and tensile testers. It was found that the as-deposited structure exhibited homogenous columnar dendrite structure, which grew epitaxially along the deposition direction. Moreover, some intermetallic phases such as Laves phase, minor MC （NbC, TiC） carbides and needle-like δ-Ni3Nb were observed in y-Ni matrix. Precipitation mechanism and distribution characteristics of these intermetallic phases in the as-deposited 625 alloy sample were analyzed. In order to evaluate the mechanical properties of the deposits, microhardness was measured at various location （including transverse plane and longitudinal plane）. The results revealed hardness was in the range of 260- 285 HVo.2. In particular, microhardness at the interface region between two adjacent deposited layers was slightly higher than that at other regions due to highly refined structure and the disperse distribution of Laves particles. Finally, the influence of precipitation phases and fabrication strategies on the tensile properties of the as-deposited samples was investigated. The failure modes of the tensile specimens were analyzed with fractography.