激光内送粉高速熔覆Cr50Ni合金稀释率及单道形貌分析

目的研究"光内送粉"正离焦高速熔覆Cr50Ni合金单道形貌及稀释率变化影响因素,制备耐磨、耐腐蚀绿色无污染的金属表面涂层,从而替代传统电镀。方法采用"光内送粉"正离焦新型耦合技术开展高速熔覆工艺试验,即在304不锈钢基体上制备Cr50Ni合金熔覆层。建立了光内送粉条件下粉末遮光模型,得出了送粉速率与粉末遮光率的关系,从而得到最终照射在基体上的激光能量,而激光能量密度与稀释率呈正相关,以此分析了不同送粉速率对熔覆层稀释率的影响,同时考察了不同离焦量对熔覆层稀释率以及单道熔覆厚度的影响,分析了最佳熔覆层的显微组织成分变化和硬度变化趋势。结果当扫描速度为9 m/min、离焦量为+1^+2 mm、激光功率为1.85 kW时,可获得厚度约为121~452μm、稀释率为12.9%~75%、硬度值为280~320HV的表面形貌较好的熔覆层。粉末粒子直径为50μm时,在16~32g/min送粉速率下,粉末遮光率为16.6%~33.1%。熔覆层底部的晶粒形态主要为明显的柱状枝晶,由于冷却速度快,进入熔池中的气体来不及逃逸,使得熔覆层内部存在一些微小气孔。结论 "光内送粉"正离焦光粉耦合新技术采用Cr50Ni合金材料,在激光功率为1.85 kW、送粉速率为28 g/min、离焦量为+2 mm、扫描速度为9 m/min的工艺参数下,可以获得理想的单道成形效果,实现高速熔覆。

加热炉中的高温灰分对金属材料的腐蚀

随着我国原油中重金属含量越来越多 ,矾引起的高温灰分腐蚀问题日益突出。文中对此种腐蚀的环境形成、腐蚀机理、耐腐蚀材料及避免腐蚀措施等方面进行了阐述。

Corrosion behavior of NiCr alloys in HCl-containing oxidation atmosphere at 700800 ℃

Corrosion behaviors of pure Ni and three NiCr alloys were investigated in an HCl-containing oxidizing atmosphere at 700 ℃ and 800 ℃. All materials suffer from accelerated corrosion at both temperatures. NiCr alloys show an initial mass loss due to the formation of volatile CrCl3 and CrO2Cl2. Some chlorides are detected at the scale/substrate interface and many voids are also found there. NiCr alloys with higher chromium content have better corrosion resistance. However, Ni50Cr is inferior to Ni25Cr due to its two-phase structure, which makes it easy for chlorine to diffuse along grain boundary and to occur inner oxidation. The relevant corrosion mechanism was also discussed.