Low Temperature Plasma Nitriding(LTPN)Technology And Its Effect On The Properties Of Duplex Treatment Of H13 Die Steel

Aluminum alloy die casting is mainly used in automobile,motorcycle engine system and running system as well as the appearance of many 3C products. Die casting mould market is huge, but its precision,life has become the technical bottleneck which restricts the development of the industry. Die casting die works in a harsh environment, It has to go through the high temperature molten aluminum melting corrosion and grinding brush. Thus how to prolong the life of die casting die has become an important engineering problem. In this paper,we firstly low temperature plasma nitriding the H13 steel by using the hollow cathode ion source auxiliary nitriding equipment, Then the CrAlN coating was prepared on the surface of the nitriding steel which is through the optimized process. Microstructure,micro hardness,bonding force,phase, surface morphology and other basic properties of nitriding and coating samples were characterized by Optical microscope,micro hardness tester,hardness tester, X ray diffraction, scanning electron microscope. Friction and wear tester and smelting furnace were used to characterize the friction and wear properties and erosion behaviors. The conclusion can be made as following:1. The efficiency of low temperature plasma nitriding which assisted by hollow cathode ion source auxiliary nitriding equipment is high, under the condition that the microstrcucture is good and the brittleness is small, we can achieve more than 50μm/ h nitrided layer. The low temperature plasma nitrided layer consist of ε-Fe_2-3N, γ′-Fe₄ N, α-Fe（N）and nitrogen rich martensite.2. Those atmosphere contained hydrogen such as H2 and CH4 are beneficial to the enhancement of the thickness of the nitriding layer. A small amount of C atmosphere can effectively reduce the harldness gradient of the cross section,and reduce the brittleness of the compound layer. the trace oxygen in the furnace is easy to react with the iron to form a layer of nano oxide film on the surface. The film can prevent the infiltration of N atoms and affect the thickness of the nitriding layer. With the help of the hollow cathode discharge, the hydrogen has a strong reduction effect,which can effectively remove the oxide film on the surface, and promote the surface Fe sputtering.3. Coating on the low temperature plasma nitriding sample can effectively enhance the binding force to HF1, in which the duplex coating which retain the compound layer is worse than that without Compound layer.4. After low temperature nitriding steel, sole and duplex CrAlN coating grinding ADC12 aluminum alloy ball. The main wear mechanism is adhesive wear, and the second is abrasive wear. Low temperature plasma nitriding and PVD coating can effectively improve the anti friction and aluminum adhesion properties. The effect of low temperature plasma nitriding on the anti friction and adhesion of aluminum is better than that of CrAlN coating. In the duplex treatment,the compound layer has a positive effect.5. CrAlN coating has excellent corrosion resistance of molten aluminum. In molten aluminum 6h will not change the composition of its phase, also the hardness will not change significantly. Single layer CrAlN coating is equivalent to the inert barrier on the substrate, and the duplex treatment is equivalent to setting a double barrier. The main failure point of the coating is the pit and the droplet. The nitriding layer of low temperature plasma nitriding steel can effectively improve the molten aluminium corrosion resistance of H13 steel, and the main failure mode of the nitriding layer is local pitting corrosion. The compound layer in the nitriding layer has a positive significance to improve the resistance to molten aluminum corrosion.