US3336120A

US3336120A - Molybdenum coated with heat-resistant alloys by casting

Info

Publication number: US3336120A
Application number: US430047A
Authority: US
Inventors: Yoda Renpei; Arai Takashi
Original assignee: DIRECTOR OF NAT RES INST OF ME
Current assignee: DIRECTOR OF NAT RES INST OF ME; DIRECTOR OF NATIONAL RESEARCH INSTITUTE OF METALS
Priority date: 1964-09-19
Filing date: 1965-02-03
Publication date: 1967-08-15
Anticipated expiration: 1984-08-15
Also published as: GB1064353A

Description

Reaper DA j .ETAL 3,336,120 MOLYBDENLYJM COATED WITH3HEAT BESISTANTIALL'QYS BY CASTING Aug. 15, 1967 2 Sheets-Sheet 2 Filed Feb.

I 70st 20m. 70100 0 41 0 A N AWE w m INVENTORS Hrai nkaslwi Renpai- /a v BYJW MW ATTORNEYS .Ue red O 3,336,120 MOLYBDENUM COATED WITH HEAT-RESISTANT ALLOYS BY CASTING Renpei Yoda, Tokyo, and Takashi Arai, Kawaguchi-shi,

Japan, assignors to Director of National Research Institute of Metals, Tokyo, Japan Filed Feb. 3, 1965, Ser. No. 430,047 Claims priority, application Japan, Sept. 19, 1964, 39/53,683 3 Claims. (Cl. 29-198) This invention relates to molybdenum coated with heatresistant alloys by casting. More particularly, this invention relates to molybdenum covered with heat-resistant alloys by applying casting and cladding.

Refractory metals having melting point much higher than iron can maintain their strength up to a high temperature but since they have drawback of being readily oxidized, they cannot be used in the atmosphere of air at a high temperature under the influence of high stress. Accordingly various protective coating methods have been heretofore proposed but they are not safe enough unless their covering layers are sufficiently strong. Since even a slightest extent of crack formed in the covering during the time of their service at a high temperature inevitably causes the ruin of the material.

Molybdenum is a representative refractory metal but it is completely lacking in anti-oxidation property. As protective coating methods heretofore applied to molybdenum, electroplating, vacuum evaporation, metallikon and cladding of oxidation-resistant metal or alloy, formation of stable refractory intermetallic compound on the surface, ceramic coating and the like can be illustrated. The method which can provide the most superior properties among above-mentioned ones is the multilayer lamination of chromium and nickel or the protective covering of MoSi utilizing the vapor deposition method.

Accordingly it is an object of the present invention to provide molybdenum covered with a heat-resistant alloy to which can readily apply such heat treatment-working in the-atmosphere of air as has been denied with prior coating treatments. It is another object of the present invention to provide molybdenum covered with heat-resistant alloys which can stand the high temperature, under the influence of high stress, in the atmosphere of air, for a long time.

These and other objects can be attained by the present invention. According to the present invention, molybdenum is covered with a heat-resistant alloy by applying simultaneously'the treatment of casting and cladding. In other words, commercially available pure round rods of molybdenum are covered by casting with Nimonic 90, a

superior nickel-base heat-resistant alloy capable of standing hot working and subsequently subjected to forgeworking to produce the protective coating.

In this case, the protective material of heat-resistant alloy is not necessarily limited to nickel-base alloy. Ironbase and cobalt-base alloys mayalso be useful so long as they can stand hot working.

With reference to the accompanying drawings, the nature of the present molybdenum coated with heat-resistant alloy is more fully depicted.

'FIGURE 1 shows photographs of macrostructure of camlachie cramped material and worked material thereof in the case when a polybdenum rod having a diameter of 3,336,120 Patented Aug. 15, 1967 5 mm. is used. Molybdenum in the central part and surrounding Nimonic alloy are perfectly jointed by fusion with each other. There is no chance of crack forming even when it is worked. It is observed that coarse columnar crystal in the camlachie cramped material are changed into fine structure.

FIGURE 2 shows the hardness distribution in the crosssection of camlachie cramped material (such similar expressions will be used hereinafter to mean material coated by casting) and worked material thereof. It is seen from FIGURE '2 that the jointed part of molybdenum with Nimonic 90 alloy by fusion has extremely high hardness and a phase of brittle compound is formed there. The hardnesses of matrix of molybdenum and that of Nimonic 90 alloy are almost the same. This phase of brittle compound consists principally of MoNi. Even when other heat-resistant coating alloy is used, the phase of molybdenum alloy becomes also a brittle one possessing high hardness. In general, the coating of molybdenum by means of the method other than cladding is readily cracked. Moreover by the cladding method, such a perfectly thick fusionjointed layer between molybdenum and coating material cannot be obtained as is the case of the present invention. Furthermore the heat treatment-working cannot be carried out freely at the high temperature in the atmosphere of air. On the other hand, the molybdenum coated according to the present invention can be freely subjected to hot working treatment at a high temperature in the atmosphere of air. There is no danger of crack forming during the time of working. This is due to the fact that thick Nimonic 90 alloy outside the layer of brittle compound perfectly prevents molybdenum from being oxidized and since it performs a function of lubricant, the phase of brittle compound can freely be deformed. This fact can also be understood from the phenomenon that non-metallic brittle inclusions existing in steel ingots are elongated in the direction of milling in steel plates. The composites material thus obtained by coating firmly the surface of molybdenum with a heat-resistant alloy, can maintain, at a high temperature, under the influence of high stress, in the atmosphere of air and for a long time, the strength which is rather superior but not inferior to those of molybdenum heretofore obtained in the experiments carried out in vacua or in the atmosphere of inert gas. This indicates the fact that the molybdenum produced according tothe present invention can maintain the perfect antioxidation 'property at a high temperaure under the influenceofhigh stress.

A more comprehensive understanding of the invention can be obtained by referring to the following illustrative example which is not intended, however, to be unduly limitative of the invention.

Example 1 whereby camlachie cramped molybdenum rods having a cross-section indicated in FIGURE 1(a) were obtained. Resulting camlachie cramped molybdenum were subor properties. When molybdenum diffused into the coating layer and the latter became rich in molybdenum or cracks were formed in the layer of molybdenum alloy or coating layer during the long time of service in the TABLE l.-VARIOUS HEAT-RESISTANT ALLOYS USEFUL IN THE COATING OF MOLYBDENUM Alloy Chemical Ni Co Fe Cr Mo W Cb Mn Si Al Ti composition Nimonic 90 N 1 base. Remainder 18 20 1. 2 8-816 00 base... Remainder 3 20 4 4 4 1 0.2 0.4 -20 Fe base 20 Remainder 25 1. 5 1 0.2

These worked specimens were machined into the test 20 pieces for creep-rupture testing having the gauge parameter of 6 mm. (in the case of molybdenum rods having a diameter of 6 mm. the gauge parameter was 7 mm.). Testing was carried out in the atmosphere of air, at a temperature of 1000 C. and under the influence of 5 kg./ mm. stress, the result of which is indicated in Table 2 and FIGURE 3.

atmosphere of air, at a high temperature and under the influence of high stress, the ruin of molybdenum perfectly lacking in anti-oxidation property surely occurs. Among various coating treatments applied to molybdenum, the multiple lamination of chromium and nickel looked most 5 promising. Also in this example, the coating with Nimonic 90; Ni-Cr alloy showed the most advantageous result in the long-time experiment.

TABLE 2.-THE RELATION BETWEEN THE DIAMETER OF CAMLACHIE ORAMPED MOLYBDENUM RODS AND THE TIME OF OREEP-RUPTURE Testing temperature: 1,000 0. Stress: 5 kg./mm. gauge parameter of test pieces; 6 mm.

1, }Chuck was broken.

With the material of Nimonic 90 alloy, the life up to the rupture was only one hour, but when molybdenum rods were inserted, the time up to the rupture increases proportionally to the diameter of molybdenum rod used. In the case of 5 mm. molybdenum, it was 864 hours, and in the case of 6 mm. molybdenum, was shown such an extent of property as the chuck of the testing machine forced the stop of testing even after the elapse of 1700 hours. The reason that the rupture time was reduced in the case of molybdenum diameter of 1 to 2 mm. is due to the fact that even small amount of molybdenum added to the matrix of Nimonic 90 alloy, becomes a kind of segregated part of coarse heterogeneous phase and the locally concentrated stress in this part accelerates the rupture. However, when the diameter of molybdenum is over 3 mm., the molybdenum and the alloy layer become to stand the stress and with the increase of diameter, the rupture time is increased proportionally.

As heat-resistant alloys capable of forge-working beside Nimonic 90 alloy, 25-20 alloy from the Fe base alloy, and S-816 alloy from the Co-base alloy were selected. Molybdenum rods having a diameter of 5 mm. were coated by casting with these alloys, subjected to 36 percent hot working and made into the same specimens as above-described. The testing was carried out in the atmosphere of air, at a temperature of 1000 C. and under the influence of stresses of 5 kg./mm. 7 kg./mm. and 10 kg./mm. whereby the result shown in Table 3 and FIGURE 4 was obtained. At the side of shorter period of time, molybdenum coated with 5-816 alloy showed superiority, and the molybdenum coated with Nimonic 90 and 25-20 alloy showed the same degree of strength. However at the side of longer period of time, Nimonic 90-coated molybdenum showed the most superi- TABLE 3.--CREEP-RUPTURE TIME OF MOLYBDENUM CAMLACHIE CRAMPED WITH VARIOUS HEAT-RESIST- ANT ALLOYS IN THE ATMOSPHERE OF AIR AT A TEMPERATURE OF 1,000 C.

Further investigation is added to the creep-rupture strength of molybdenum covered with Nimonic 90. The above-mentioned specimens consist of three parts; the central part of pure molybdenum, the surrounding part of molybdenum alloy layer, and the outside part of coating layer of Nimonic having the thickness of about 0.7 mm. The strength of Nimonic can, as seen from Table 3 or FIGURE 3, be neglected at the instanced condition of the test. When assumed that the rupture strength is only dependent upon the molybdenum part, and when 5 kg./mm. of stress is loaded on the specimens as shown in Table 4 and with dotted lines in FIGURE 5, then in the part of molybdenum diameter less than 3 mm., the stress exerted on this part increases abruptly with the reduction of molybdenum diameter, but in the part of molybdenum diameter more than 4 mm., the relation of stress exerted on the molybdenum part to rupture time becomes linear as shown by the dotted straight line, regardless of how much the stress is. As the result of this, it is not proper to say that the creep-rupture strength is only dependent upon the strength of molybdenum part in the specimens when this part is much too small. In reality, the rupture strength of specimens is dependent upon the parts including both molybdenum and molybdenum alloy layer. This fact can be understood from the linear relationship of the strength of molybdenum and molybdenum alloy layer to the rupture time as shown in Table 4 and by the solid line in FIGURE 5, irrespectively of the size of molybdenum diameter and the value of stress.

Molybdenum having such characteristic properties has never been obtained heretofore by any prior treating methods.

What is claimed is:

1. A composite material, capable of being subjected to hot working in air, consisting of a molybdenum core and a heat-resistant alloy coating material, said coating consisting essentially of a composition of approximately 18 percent by weight of cobalt, percent by weight of chromium, 1.5% by weight of aluminum, 2% by weight of titanium and a remainder of nickel.

TABLE 4.THE RELATION BETWEEN THE STRESS EXERTED UPON MOLYBDENUM PART AND MOLYBDENUM AND MOLYBDENUM ALLOY LAYER PARTAND THE CREEP- TIME IN THE SPEOIMENS OF MOLYBDENUM COVERED WITH NIMONIC 90 Actually Actually Stress upon Stress upon Stress upon the measured measured actually actually parallel part 0! Diameter of diameter of diameter of measured measured Creepspecimens Mo rods camlachie Mo+Mo diameter of diameter of rupture (kg/mm!) used (mm.) cramped alloy layer Mo Mo+Mo time (hr.)

Mo (mm.) (mm) (kg/mm!) alloy layer g./mm.=)

In FIGURE 5, triangular marks show the rupture strength of pure molybdenum tested at a temperature of 982 C..in vacua at 10, 100 and 1000 hours. These points almost coincide with the solid line which indicates that the novel coating treatment with the Nimonic 90 alloy is protecting the molybdenum perfectly from oxidation in the atmosphere of air at a high temperature and under the influence of stress.

The molybdenum produced according to the present invention have several characteristic points. Firstly the brittle alloy layer can be worked with molybdenum without fear of being cracked. Secondly since the recrystallization temperature is 1150" to 1200 C., it is possible to strengthen molybdenum by strain hardening if the working is carried out at a temperature lower than the above-mentioned temperature. Thirdly there is no need of the inactive atmospheric furnace and the vacuum furnace for heating molybdenum. It can be freely worked in the heat treatment in the atmosphere of air. Fourthly even when imperfectly fusion-jointed part exists locally in the carnlachie cramped state, it can be brought to the sound state by the subsequent hot working treatment. Fifthly it is possible to maintain molybdenum in the atmosphere of air at a high temperature, under the influence of stress for a long time.

2. A composite material, capable of being subjected to hot working in air, consisting of a molybdenum core and a heat-resistant alloy coating, said coating consisting essentially of a composition of approximately 20 percent by weight of nickel, 3 percent by weight of iron, 20 percent by weight of chromium, 4 percent by weight of tungsten, molybdenum and columbium, one percent by weight of manganese, 0.2 percent by weight of silicon, 0.4 percent by weight of carbon and a remainder of cobalt.

3. A composite material capable of being subjected to hot working in air, consisting of a molybdenum core and a heat-resistant alloy coating, said coating consisting essentially of a composition of approximately 20 percent by weight of nickel, 25 percent by weight of chromium, 1.5 percent by weight of manganese, one percent by weight of silicon, 0.2 percent by weight of carbon and a remainder of iron.

References Cited UNITED STATES PATENTS 2,924,004 2/1960 Wehrman 29-198 3,044,156 7/1962 Whitfield 29-198 X 3,066,393 12/1962 Malagari 29-198 HYLAND BIZOT, Primary Examiner.

Claims

1. A COMPOSITE MATERIAL, CAPABLE OF BEING SUBJECTED TO HOT WORKING IN AIR, CONSISTING OF A MOLYBDENUM CORE AND A HEAT-RESISTANT ALLOY COATING MATERIAL, SAID COTAING CONSISTING ESSENTIALLY OF A COMPOSITION OF APPROXIMATELY 18 PERCENT BY WEIGHT OF COBALT, 20 PERCENT BY WEIGHT OF CHROMIUM, 1.5% BY WEIGHT OF ALUMINUM, 2% BY WEIGHT OF TITANIUM AND A REMAINDER OF NICKEL.