Cellular microstructure modification and high temperature performance enhancement for Sm2Co17-based magnets with different Zr contents

Influence of Zr contents on high-temperature magnetic performance of Sm(CoFeCuZr)(x=0.025,0.03,0.035,0.04) magnets were investigated.As x increases from 0.025 to 0.04,the temperature coefficient of intrinsic coercivity(H) is optimized from-0.1673% K^(-1)to-0.1382% K^(-1)and the Hat 773 K gradually increases from 556.32 kA m^(-1)to 667 kA m^(-1).The microstructure and microchemistry of different Zr-content magnets were revealed by a transmission electron microscope equipped with EDS.The increasing Zr content induces that the average size of cells decreases from ~76 nm to ~56 nm and the weight fraction of 1:5 H cell boundary phase increases from ~25% to ~37% as well,resulting decreasing of the average Cu content at cell boundaries from 13.59 at% to ~8.52 at%.It is found that the Cu-lean characteristic at cell boundary phase is the reason that gives rise to higher magnetic properties at elevated temperatures for x=0.04 magnet.

Effect of Zr content on crack formation and mechanical properties of IN738LC processed by selective laser melting

Two batches of commercial IN738LC alloy powders with different Zr contents were printed under the same parameters.The influences of Zr content(0.024 wt.% and 0.12 wt.%,respectively) in powders on crack density,distribution,formation mechanism and mechanical properties of selective laser melting(SLM)-treated parts were systematically studied.It was found that the crack density(area ratio) increases from 0.15% to 0.87% in the XOY plane and from 0.21% to 1.81% in the XOZ plane along with the Zr content increase from 0.024 wt.% to 0.12 wt.% in the original powders.Solidification cracks are formed along the epitaxially grown <001>-oriented columnar grain boundaries in molten pool center.The ultimate tensile strength of Sample 1(0.024 wt.% Zr) is 1113 MPa,and there are dimples in tensile fracture.With an increase in the Zr content to 0.12 wt.%(Sample 2),the ultimate tensile strength of Sample 2 decreases to 610 MPa,and there are numerous original cracks and exposed columnar grain boundaries in tensile fracture.The optimization of printing parameters of Sample 2 considerably increases the ultimate tensile strength by 55.2% to 947 MPa,and the plasticity is greatly improved.

New Ti-Zr-Cu-Ni-La system brazing filler metals for the joining of titanium alloy

In order to research the influence of Zr content （ below 15 wt. % ） on the properties of the filler metal. Ti-5Zr- 15Cu-15Ni-La, Ti-lOZr-15Cu-15Ni-La and Ti-15Zr-15Cu-15Ni-La filler metals were prepared. The wettability of the filler metals on Ti-6Al-4V was evaluated and the melting temperatures of the filler metals were tested by differential scanning calorimetry （DSC）. The microstructures and mechanical properties of the brazed joints were investigated. The results show that the wettability of the filler metals improves as the Zr content increases. Zr content has great influence on the melting temperature of the filler metals. When Zr content changes from 5 wt. % to 10 wt. % and 15 wt. % , the melting temperature decreases about 80 ℃. The brazed joint with Ti-5Zr-15Cu-15Ni-La filler metal shows aciculate phase on the interfizce. The brazed joints with Ti-lOZr-15Cu-15Ni-La and Ti-15Zr-15Cu-15Ni-La filler metals consist of three zones, a segregated center zonc, diffusion reaction zone and acicular zone. The brazed joint with Ti-5Zr-15Cu-15Ni-La filler metal achieves the maximum shear strength 313.9 MPa.

Experimental study and cellular automaton simulation on solidification microstructure of Mg-Gd-Y-Zr alloy

The solidification microstructure of Mg-Gd-YZr alloy was investigated via an experimental study and cellular automaton(CA)simulation.In this study,stepshaped castings were produced,and the temperature variation inside the casting was recorded using thermocouples during the solidification process.The effects of the cooling rate and Zr content on the grain size of the Mg-Gd-Y-Zr alloy were studied.The results showed that the grain size decreased with an increase in the cooling rate and Zr content.Based on the experimental data,a quantitative model for calculating the heterogeneous nucleation rate was developed,and the model parameters were determined.The evolution of the solidification microstructure was simulated using the CA method,where the quantitative nucleation model was used and a solute partition ceoefficient was introduced to deal with the solute trapping in front of the solid-liquid(S/L)interface.The simulation results of the grain size were in good agreement with the experimental data.The simulation also showed that the fraction of the eutectics decreased with an increasing cooling rate in the range of 2.6-11.0℃·s^(-1),which was verified indirectly by the experimental data.