Weakening affinity of SUS304 asperities to die surface with TiN coating for preventing delayed cracks in deep-drawn cups

SUS304 stainless steel has strong affinity to carbon tool steel surfaces. Therefore, the flow of material in the flange portion during the deep drawing process is retarded, leading to increase in amount of wall thicknening along the cup edge and rising risk for delayed cracks. In this paper, TiN coating is applied to the drawing die surface to weaken the affinity. Under elevated blank holding forces (BHF), the experimental results showed that the crack-free BHF range for the TiN coated and the uncoated dies are 5~10 kN and 12 kN, respectively. The entire BHF range for successful drawn cups formed with the coated die are crack-free. The crack-free BHF magnitude is successfully lowered and the range is enlarged with the coating. Crack-free cups having large elongated height and low amount of wall thickening along the cup edge are formed. The weak affinity is evidenced by the low estimated coefficient of friction (COF) obtained from a FE simulation model based on the Coulomb’s law of friction. In contrast, the estimated COF of the uncoated die is high even at the low BHF due to the strong affinity. Therefore, delayed cracks are observed under BHF range of 7~11 kN. At BHF of 12 kN, wear fragments are formed in the boundary layer as a result of the continuous polishing of the SUS304 asperities by the uncoated die asperities. The COF is sharpyly decreased due to the smooth relative movement of contacting surfaces facilitated by the particles and the formation of cracks is prevented. However, the segments tend to penetrate into the SUS304 surface under excessive BHF of 13kN and above. The relative motions of the segments are prohibited, resulting in the reformation of the cracks.

Experimental Study on the Influence of AC Stray Current on the Cathodic Protection of Buried Pipe

The size of the damaged area of the coating and its position on the pipeline impacted the cathodic protection potential, and there was a damaged area of the greatest impact value. When damaged area was 300 mm2, the IR drop was the largest, and this situation could easily lead to inadequate protection; when the parallel spacing between pipeline and interference source was unchanged, the measured value curves of cathodic protection potential presented “U” shaped trend with the increasing stray current interference intensity. Under certain parallel spacing between pipeline and interference source, high alternating stray current intensity would cause serious negative offsets, so that the overprotection of the pipeline occurred, and make the coating crack; there was a parallel threshold length. When less than the threshold, the pipe-ground potential increases rapidly with the parallel length increasing. In order to judge whether a pipeline was interference by AC stray current and the risk of stray current corrosion, we should make a comprehensive analysis of the cathodic protection energizing potential, the switch-off potential, AC pipe-soil potential, IR drops, and so on.

Finite Element Analysis of Coating Interface Stress Field of Laser Cladding CBN Coating on Titanium Alloy

Laser cladding technology is used to prepare TC11 titanium alloy surface coated CBN. Through the finite element method to simulate the movement of scratch experiment. When coating is under normal force and tangential force, through changing the thickness of the layers , the coating crack length and width of crack, coating in force is analyzed when the interface stress affects on coating.Simulations that the interface stress value of 0.2mm coating reach to 1.485Gpa, The interface stress value of 0.5mm crack length reach to 0.3707Gpa, The interface stress value of 0.06mm crack width reach to 0.2234Gpa.

Influence of Aluminide Coating on Fatigue Behavior of a Nickel Superalloy

The influence of the technology and the thickness of an aluminide coating on mechanical fatigue of a nickel-alloy at 700°C has been studied. It was shown that the brittleness and the surface roughness of coating were the basic causes to the earlier rupture of a system. The thicker coating, the more harmful to fatigue performance. The mechanism of influnece of coating on metal fatigue and the possibility to estimate fatigue life of coating/alloy system were also discussed. It is believed that the stress concentration caused by coating crack accelerated substrate alloy to rupture.

A Fracture Mechanics Approach to Turbine Airfoil Design

An analytical study was conducted using fracture mechanics principles to model turbine airfoil cracking. It was found that crack initiation can be related to calculated residual strains in the airfoil coating and that coating properties are an important consideration in determining crack location and orientation. The coating crack subsequently propagates into base material according to basic fracture mechanics laws. A comparison with engine tested blade experience is made. It is concluded that the presented model provides a rational method for design life prediction but its general application requires definition of new types of material property information.