US2437409A - Activating and electroplating stainless steel - Google Patents

Description

j UNITE-D Patented Mar. 9, :1948 p Eastman Kodak Company, Rochester, N. Y., a M corporation of NewJerseyf Y r lflo l lrawin13,v Applicatlon'August22 1945,.y I; k a I. 1 t stre 13 f l. 1 5 Claims. 204 -49)- invention rela es 1' to" electroplating, and '2 menced. This,of course,'seriously hampers promo p t larly to'electropla i 'ad nt el duction on a commercial scalewhen using standtrodepesits ofmetals on-alloyssuch stainless ard types of apparatus; 1A directresult of the steels and other alloyspossessing-a high order of *restoration'of the'passive beforeftheplatin Egrrosionresistance-which: is generally" attrib- 5 operation is'bomrriericed is-a poor option-adhertableto the presence ofsuch allqying elements ing electro-d'eposit. I An object therefore, of the as-chromium, nickel; ,co1umbium and tungsten. present invention is'toipiovide a plating process i-here are many instances where it; is desired whereby thenormally,passive surfaces of various toplate copper, nickel and other metals on alloys alloys can be"changedftb aetivefsurfacs which containing the above-mentione'dalloying metals. 10 will prevail Sumci auy -1 nge erm t leisurely im fq e ve bcerrid'evisedto reduce the transferof such alloy artlcles from-the activatin corrosion resistance pf these alloys and thereby solution to' the plating bath 'before'sel f restorato provide &1? atiyefsiu rface which will take an 'tion of the passive surface occurs. electrodepos'it u Some'suc'h alloys may be suitably fAn other' 'ebject bf the 'irrvention is a'comm'eractivat edby-eithen anodicand/or cathodic treatciallvoperable" plating process 'for plating alloys ment iii-acid solutions-or'varyin'g concentration having normally passive surfaces.

Typical of such acid solution processes is 'eath- Stillanother bbject is-a'cemmeman operable "oa-iclactivaitioh 1111: more t n 0% bi w -g tisulplating process for plating alloys having normalfui-ic'aid;=anodicactivationfin"approximately ly passive surfaces whichwill give deposits of 110%" by'weigl'it hydroehlorici acid and anodic greatly improved adherence as well asjthickness. Processing inf%-- by weight ortho phosphoric In' accordance yvitltthe'iriveiitidri" nest; and acid;{Theinstant invention'relatesmore directother objects *are" attained by" electrol" the m-how v r; t9 themore' passive-types of alloys article to be"plated; 'which-"comprises alloy such S Ype 302, 304=,'309,"316,317, 321, and 347 having a passivesllrfac',"in an'acidbath contain- -stainlesssteels, Hastello'ys, Inconel; Worthite 25 mg a metal halidtoproduce an active film on Durimet, et'cJ- These'alloy's may be suitabl actithe alloysurfaee. The article-remade'the cath vated --by comparatively high eurr ne density odein the bath an initial current *o'f relastrikin'g, or plating in highly acidic solutions of tively high amperage-per ='unitof"cathode area :copper; or preferably nickel salts, containing (3011- is applied thereto for -a' relatively sh'ort period siderablequantities-of acidssuch'as hydrochloric, and then the current -preferably without inter- :phosphoric, sulfamic and sulfuric. The amount 'ruption,--is reduced-tea lowervalue per unit of 'of;a cid employed in theseiprocesses tends to drop cathode area and is applied for a, relatively longer the efliciencycf the:metal deposition to less'than period. This treatment activates the passive sur- 10%, Under such special circumstances it is face of' the alloyandplaees a metal film over the possible. to produce a satisfactory degree of suractive surface to 'which other metals maybe fage ..-.act ivatlon-. on the normally. passive alloy plated by'known'methods. I have found that the article to be plated. While .such treatments satactive surface producedin this manner in accordisfactorily actlvatethe passivealloy surface, unance with my invention will retain its activity fortunately the activated surface prevails; only for-avery considerable time}; A fully activestate, for a few minutes and it has been found-thatthe 40 which yielded deposits of excellent adhesion, pa i e ;fi,1 m surface is automatically, restored i could be maintainedfor- 10 minutes; To aid furafterjthis ti ge, n. .tl .e,. case o1: small;artic1es, theriin the llfetentionaofjhe activesurface i-c this self-:restoration ofthe passive filmmaynot duced by my process the activated surface may interfere too much with the subsequent plating be kept wet with thestrikesolution or cold water. operation l I loiveyer, yvhen relatively large arti- 5 My studies conclusively indicate that the high 9 55 1? ctivated, the eterioration of the active to current density strike followed by the prolonged surfaceand the'simultaneous partial or complete low currentjdensity strike .is responsible for the restoration of the passive. surface frequently ocgreatly increased time that the active surface will n sbem e. thearticl can be transferred to the Prevail; 7' v t b r e; V

" com- The invention isimrer fintedjntmoredetail in.

Plate at e in? the following examples which show typical processes for achieving excellent adhering electrodeposits on alloys which normally resist electroplating and, therefore, cause poor or non-adhering deposits.

Example I followed by continuation of the striking process without current interruption at 25 to 30 amperes occur even though the thin nickel strike film is on the alloy, after a relatively short period.

It will be understood by those skilled in the art that the piece to be plated is suitably degreased or otherwise cleaned as may be necessary before the strike operation. Such cleaning operations may include scouring with lime and acid or alkaline treatment to remove scale, etc.

The process thus described is applicable to all the'alloys herein mentioned and after the nickel strike has been deposited on the alloy its active surface will also be receptive to copper or other metal plating as will be understood by those skilled in this art.

Iclaim: 1. The method of activating, and prolonging that activation, of the surface of stainless steel alloys having normally a passive surface which per square foot for 15 to 30 minutes. It was found that the alloy surface changed from a passive surface to an active surface and retained its activity for at least 10 minutes. This permits the operator to remove the article from the initial bath and properly install it in the subsequent bath where it received a permanent electrodeposit of nickel, according to the process shown in my U. S. Patent 2,147,415 of Feb. 14, 1939. The nickel plated on the alloy was found to have excellent adhesion and was in general satisfactory for most 1 uses.

Where severe mechanical operations, such as drilling, turning, milling, etc. are contemplated and particularly when such operations Will penetrate through the interphase between the deposit and the substrate metal, I prefer to supplement the above described process by a low temperature anneal at 400 F. to 1200" F. :The low temperature anneal seems to enhance the resultant adhesion probably because it eliminates or reduces the strains resulting from adsorption or occlusion of atomic hydrogen originating in the prolonged striking operation.

Example II A modification of the process described in Example I was tried in which the initial strike was conducted at a voltage yielding 100 amperes per square ;foot on thecathode for 2 to 4 minutes followed by continuation of the striking process without current interruption at 25 to 50 amperes .per square root for 15 to 30 minutes. The actibetween 100 and 300 a-mperes for 2 to 4 minutes and the final lower amperage employed may be between 15 and50 amperes per square foot of cathode area for 15'to 30 minutes.

When plating large pieces that require 'm'echanica1 transfer from the strike bath to the subsequent plating bath and maytake-upward's of 10 minutes, the piece may be kept wet with cold water or a portion of the nickel 'str i'ke solution so that the passive surface will not restore itself before the transfer isefie'ct edu It should be understood that deterioration of the active film will comprises making the alloy the cathode in an electrolytic bath composed essentially of nickel chloride and hydrochloric acid, electrolyzing the bath at a current of 100 to 300 amperes per square foot of cathode area for 2 to 4 minutes followed by a continuation of the electrolyzing at 15 to 50 amperes per square foot of cathode area for 15 to 30 minutes, whereby an active surface is established on the alloy which will persist for a substantially long period.

2. The method of activating, and prolonging that activation, of the surface of stainless steel alloys having normally a passive surface which comprises making the alloy the cathode in an electrolytic hath composed essentially of nickel chloride and hydrochloricacid electrolyzing the bath at 200 amperesper square foot of cathode area for 2 minutes followed by a continuation of the electroly'zi'ng without current interruption at 25 to 5'0 amperes per square foot of cathode area for '15 minutes, whereby an active surface is established on the alloy which will persist for 10 minutes, 1

3. The method of activating and plating the surface of stainless steel alloys having normally a passive surface which comprises making the alloy the cathode in an electrolytic bath composed essentially of nick-e1 chloride and hydrochloric acid, .electrolyzing the bath at 100 to 300 amperes per square foot of cathode area for 2 to 4 minutes followed by a continuation of the electrolyzing at 15 to 50 amperes per square foot for 15 to 30 minutes, whereby an active surface is established on the alloy, and then increasing the .plate thickness in a second plating bath before the active surface changes to a passive surface.

4. The methodof activating and plating the surface of stainless steel alloys having normally a passive surface which comprises making the alloy the cathode in an electrolytic bath composed essentially of nickel chloride and hydrochloric acid electrolyzin'g the bath at 200 amperes per e NiClz-Hzo' and 16 ounces per gallon of 1.18 spe cific gravity hydrochloric acid electrolyzing the REFERENCES CITED The following references are of record in the file of this patent:

Um'mn STATES PATENTS Number Name Date 2,069,566 Tuttle Feb. 2, 1937 2,285,548 Wesley June 9, 1942 2,358,995 Pinner Sept. 26, 1944 OTHER REFERENCES Transactions of the American Electrochemical 1 Societm'Apr. 1915, pages 144-154, vol. 27.