A Comparison of the Microstructure, Mechanical Properties, and Corrosion Resistance of the K213 Superalloy after Conventional Casting and Selective Laser Melting

Abstract

K213 superalloy was fabricated by conventional casting and selective laser melting (SLM). The microstructures of the two samples were examined, and the mechanical properties and corrosion resistance of these two kinds of K213 alloy were comparatively studied. The results show that segregation of Ti occurs at the grain boundaries of the as-cast alloy, resulting in the formation of MC carbide. Many microcracks were formed in the SLM sample. Premature fracture of the as-cast alloy is caused by the precipitation of the harmful phase (Ti, Mo, Nb)C (MC). The MC carbides and microcracks in the as-cast and SLM alloys, respectively, induce tensile fracture. In comparison, the strength of the SLM sample is greater, while the elongation of the as-cast sample is greater. The oxidation resistance of the SLM sample is better at a high temperature of 800 °C. This is due to the relatively uniform composition and microstructure of the SLM alloy. However, the corrosion rate of the SLM alloy is accelerated during the electrochemical immersion corrosion process due to the existence of microcracks.

Comparative Study on Passive Film Formation Mechanism of Cast and PBF-LB/M-TC4 in Simulated Physiological Solution

“…Four cathodic current peaks can be detected in the reverse scanning, among which c 1 (1.9 V SCE ), c 2 (−0.3 V SCE ) and c 3 (−0.87 V SCE ) are the reduction peaks of a 4 and a 5 , and a 3 and a 2 , respectively. Due to the dissolved oxygen having a strong reduction reaction and reaching its limit at −0.6 V SCE [ 28 ], part of the reduction process signal of Ti 4+ /Ti 2+ /Ti could be covered up, resulting in an insignificant reduction peak. The a 3 peak is the highest and the c 2 peak can be observed, indicating that the film is mainly Ti 4+ [ 27 ].…”

“…The model considers the passive film layer ( R f , Q f ) and in series the charge transfer layer ( R ct , Q dl ), where R s is the solution resistance, R f and Q f are the passive film resistance and related double-layer constant phase element and R ct and Q dl are the charge transfer resistance and related electrical double-layer constant phase element, respectively. In general, capacitance is non-ideal due to the electrode surface roughness [ 27 , 28 , 29 , 30 ], which can be written as [ 30 , 31 , 32 , 33 ] where ω , j and n are the imaginary unit, angular frequency and exponent, respectively, and the constant phase element is equal to the capacitance while n = 1 [ 27 , 28 , 29 , 30 , 31 , 32 , 33 ].…”

“…where ω, j and n are the imaginary unit, angular frequency and exponent, respectively, and the constant phase element is equal to the capacitance while n = 1 [27][28][29][30][31][32][33]. The R f of two TC4 increases rapidly from 10 5 Ω•cm 2 (0.5 h) to 10 6.3 Ω•cm 2 (12 h) and then fluctuates around 10 6.3 Ω•cm 2 for cast-TC4 (see Figure 8c).…”