The effect of heat treatment and extrusion process on microstructure evolution, mechanical properties and corrosion behaviors of as-cast Mg-Dy-Ni alloy were systematic investigated. Results show that hot extrusion and heat treatment can greatly refine the microstructure and facilitate the redistribution of the second phase respectively, resulting in significant changes in corrosion behaviors. Network distribution LPSO phase with bulk Mg 6 Ni phase scatters distribution in the as-cast sample, which destroys the network structure and thus accelerates the corrosion rate of LPSO phase and Mg matrix. While, after the heat treatment, network distribution LPSO phase accompanied by a large amount of Mg 6 Ni phase uniform distribution forming the corrosion barrier to inhibit the corrosion propagate. After extrusion, streamlined distribution strip LPSO phase with broken Mg 6 Ni phase destroyed the overall structure of strip LPSO phase and reduced the corrosion barrier in the ED sample to provide high corrosion rate than TD sample. While, the LPSO phase and grain refinement after extrusion to provide a denser corrosion product film to slow down the corrosion in TD sample. Moreover, the highest corrosion rate was obtained in the as-cast sample with 66.1 mg.cm -2 .h -1 in 3 wt % KCl solution at 25 ℃, while the highest mechanical properties and moderate corrosion properties were achieved in the ED sample with ultimate compressive strength 536 MPa and 29.3 mg.cm -2 .h -1 in 3 wt % KCl solution at 25 ℃, respectively. Which not only broadens the Mg-RE-Ni system alloy applications for fracturing tools, but also provides a reference for the design of the full chain of high strength and high degradation alloy.
Different solution treatments were carried out on the semi-continuously cast Mg-9.55Gd-2.27Y-1.28Zn-0.55Zr-0.11Nd (wt.%) alloy at temperatures of 480 °C, 500 °C, and 520 °C. It was found that the different solution treatment temperatures led to different phase constitutions of the alloy. The Mg3RE-type eutectic phases transform into long period stacking order (LPSO) phases with various morphologies after solution treatment. Increasing the solution temperature resulted in larger grain size, greater number of lamellar LPSO phases, and segregation of Zr element. Block LPSO phases also shifted to rod LPSO phase. After ageing treatment, the special spatial structure consisting of prismatic β′ precipitates, basal γ′ precipitates, and lamellar LPSO phases hindered dislocation movement effectively, leading to high strength. However, the accumulation of massive dislocations promoted the premature formation of cracks at the grain boundary and LPSO/Mg matrix interface, resulting in a rapid decrease in ductility of the alloy. After solution treatment at 480 °C for 12 h and aged at 200 °C for 48 h, the Mg-9.55Gd-2.27Y-1.28Zn-0.55Zr-0.11Nd alloy exhibited favorable comprehensive mechanical properties at room temperature: ultimate tensile strength (UTS) of 383 MPa, tensile yield strength (TYS) of 269 MPa, and fracture elongation (EL) of 5.1%.
This paper presents experimental work on studying the detailed structure and strain relaxation of nanometer thick Nd 2 O 3 films epitaxially grown on Si(111) substrates using molecular beam epitaxy (MBE). Investigations by various diffraction methods demonstrate that the Nd 2 O 3 layers exhibit a well-ordered cubic bixbyite structure with a single orientation, perfect crystallinity and a sharp interface. The epitaxial relationship between the Nd 2 O 3 layer and the Si substrate is [111] Nd2O3 //[111] Si and [1-10]Nd 2 O 3 //[-110] Si . Three-fold in-plane symmetry is observed by both in-situ reflection high-energy electron diffraction after growth and ex situ X-ray diffraction Phi-cone scans. By two orthogonal X-ray diffraction scans with high resolutions, the out-of-plane and in-plane lattice mismatches between an 8 nm Nd 2 O 3 layer and Si substrate were precisely estimated to be 3.25% and 0.66% (if we consider two Si unit cells), respectively. We conclude that the 8 nm Nd 2 O 3 layer is partially relaxed with a compressive strain of -1.32% in the in-plane direction and a tensile strain of 1.22% in the out-of-plane directions.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)