Preparation And High Temperature Oxidation Resistance Of NiCrP Amorphous Alloy Coating

In this paper,NiP and NiCrP amorphous alloy coatings were prepared by electrodeposition on copper substrates.The optimum plating process was obtained by orthogonal test and single factor test.The effects of different technological conditions on the surface morphology,micro-area composition and structure of the coatings were studied by means of scanning electron microscopy（SEM）,energy dispersive spectrometry（EDS）and X-ray diffraction（XRD）.Differential scanning calorimeter（DSC）and thermogravimetric analysis（Tg）were used to study the thermal stability and high temperature oxidation resistance of alloy coatings,and the mechanism of oxidation resistance was explored.The effects of various factors on the composition and deposition rate of Electrodeposited NiCrP amorphous alloy coating are determined by orthogonal test.the effect on the deposition rate of the coating is as follows:Temperature>pH>CrCl₃>Current density>NiSO₄;The effect on the content of Cr element in the coating is as follows:CrCl₃>Temperature>pH>Current density>NiSO₄.The optimum preparation technology of Electrodeposited NiCrP amorphous alloy coating was determined by single factor experiment.That was as shown:CrCl₃·6H₂O100g/L,NiSO₄·7H₂O 5g/L,NaH₂PO₂·H₂O 1g/L,NaBr 15g/L,NH₄Cl 50g/L,KF 1g/L,C₇H₅O₃NS 0.5g/L,H₃BO₃ 30g/L,C₆H₄SO₂NNaCO·2H₂O 3g/L,Na₃C₆H₅O₇·2H₂O 80g/L,HCOOH 40mL/L,pH=3.5,Current density 150mA/cm²,Temperature 30℃.The results show that:the XRD patterns of alloy coatings with different compositions were found to have diffuse scattering peaks around 2θ≈45°,showing an amorphous structure;By analyzing the DSC,the crystallization temperature of NiP amorphous alloy is about344℃,and when the content of Cr element in the coating（wt.%）is 0.8%to 1.8%,the crystallization temperature range of NiCrP amorphous alloy coating is 375⁴03.5℃.It indicates that the introduction of Cr can increase the crystallization temperature of the amorphous alloy coating,and the crystallization temperature increases with the increase of Cr content.By calculation of oxidation activation energy,the oxidation activation energy of NiP amorphous alloy is calculated to be 1.54×10³ J/mol,Ni0.5CrP is 8.16×10³ J/mol,Ni0.8CrP is 2.83×10⁴ J/mol,Ni1.8CrP is 3.53×10⁴ J/mol,it is found that the addition of Cr also has a significant improvement in oxidation resistance,and the high temperature oxidation resistance increases with the increase of Cr content in the coating.When the content of Cr in the coating is 1.8%（wt.%）,the high temperature oxidation resistance is best.XRD patterns at different temperatures indicate that the high temperature oxidation resistance is due to the formation of a dense oxide film of Cr in the coating.