ASTM B920-16
用次氯酸钠溶液蒸气测定金属基底上金和钯合金涂层孔隙率的标准实施规程

Standard Practice for Porosity in Gold and Palladium Alloy Coatings on Metal Substrates by Vapors of Sodium Hypochlorite Solution

被代替

标准号

ASTM B920-16

发布

2016年

发布单位

美国材料与试验协会

替代标准

ASTM B920-16(2022)

当前最新

ASTM B920-16(2022)

 

 

引用标准

ASTM B374 ASTM B542 ASTM B735 ASTM B741 ASTM B765 ASTM B798 ASTM B799 ASTM B809

适用范围

5.1 Palladium and gold coatings are often specified for the contacts of separable electrical connectors and other devices. Electrodeposits are the form of gold that is most used on contacts, although it is also employed as inlay or clad metal and as weldments on the contact surface. The intrinsic nobility of gold and palladium alloys enables it to resist the formation of insulating oxide films that could interfere with reliable contact operation.

5.2 In order for these coatings to function as intended, porosity, cracks, and other defects in the coating that expose base-metal substrates and underplates must be minimal or absent, except in those cases where it is feasible to use the contacts in structures that shield the surface from the environment or where corrosion inhibiting surface treatments for the deposit are employed. The level of porosity in the coating that may be tolerable depends on the severity of the environment to the underplate or substrate, design factors for the contact device like the force with which it is mated, circuit parameters, and the reliability of contact operation that it is necessary to maintain. Also, when present, the location of pores on the surface is important. If the pores are few in number and are outside of the zone of contact of the mating surfaces, their presence can often be tolerated.

5.3 Methods for determining pores on a contact surface are most suitable if they enable their precise location and numbers to be determined. Contact surfaces are often curved or irregular in shape, and testing methods should be suitable for them. In addition, the severity of porosity-determining tests may vary from procedures capable of detecting all porosity to procedures that detect only highly porous conditions.

5.4 The present test practice is capable of detecting virtually all porosity or other defects that could participate in corrosion reactions with the substrate or underplate. In addition, it can be used on contacts having complex geometry such as pin-socket contacts (although with deep recesses it is preferred that the contact structures be opened to permit reaction of the vapors with the interior significant surfaces).

5.5 The relationship of porosity levels revealed by particular tests to contact behavior must be made by the user of these tests through practical experience or by other forms of testing. Thus, absence of porosity in the coating may be a requirement for some applications, while a few pores in the contact zone may be acceptable for others. The acceptable number, sizes and locations of the pore corrosion products shall be as specified on the appropriate drawing or specification.

5.6 This test is considered destructive in that it reveals the presence of porosity by contaminating the surface with corrosion products and by undercutting the coating at pore sites or at the boundaries of the unplated areas. Any parts exposed to this test shall not be placed in service.

5.7 The test is simple and inexpensive. The cost associated with the test is very low, using standard basic equipment found in an industrial laboratory. There are minimal waste disposal issues associated with the procedure. The test is very popular because of its very quick means of assessing the likelihood of......

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