Ni-Mo-Cr-B Alloys: Corrosion Resistant Amorphous Hardfacing Coatings
- PDF / 1,340,317 Bytes
- 5 Pages / 417.6 x 639 pts Page_size
- 67 Downloads / 237 Views
Ni-Mo-Cr-B ALLOYS:
CORROSION RESISTANT AMORPHOUS HARDFACING COATINGS
S. K. DAS, E. M. NORIN*, AND R. L. BYE Allied Corporation, Materials Laboratory, Cbrporate R&D, P.O. Box 1021R, Morristown, N. J. 07960, *Metglas) Products, Allied Corporation. ABSTRACT A series of rapidly solidified Ni-Mo-Cr-B alloys have been investigated for possible application as corrosion resistant hardfacing coatings. As-cast amorphous ribbons were pulverized to powder, which was subsequently applied to a substrate by plasma spraying. The coatings are substantially amorphous, as revealed by x-ray diffraction and transmission electron microscopy. They exhibit -95% of theoretical density and exhibit good corrosion and wear resistances, superior to those of many commercially available hardfacing coatings. INTRODUCTION It has been recognized for some time that metallic glasses formed by rapid solidification processing have little application as structural materials [1]. I-bwever, recent work at Allied Corporation has shown that certain devitrified metallic glasses, when consolidated into bulk compacts, exhibit outstandinq properties [2]. In particular, a class of Ni-Mo-B alloys has been developed, which exhibits good hot hardness and wear resistance properties [2]. It has been found that when many of these amorphous alloys are plasma sprayed onto a substrate, the resulting coatings remain substantially amorphous. This is not totally surprising, since plasma deposition is known to provide high cooling rates and has been investigated as a method of making rapidly solidified bulk parts [3]. In the present paper, we report on the corrosion resistances of a class of Ni-Mo-Cr-B amorphous alloys and their application as plasma sprayed hardfacing coatings. EXPERIMENTAL The alloys investigated in the present study were rapidly quenched from the melt into continuous ribbons using either jet casting or the Planar Flow Casting (PFC) process [1]. The ribbons were pulverized to -80 mesh powder and plasma sprayed onto a steel or altuinun substrate using a MET(CO 7MB plasma gun. Both the as-cast ribbons and coatings were checked for crystallinity using x-ray diffraction and transmission electron microscopy. Electrochemical corrosion tests were carried out on the as-cast ribbons in IN H2SO4 at 30 0 C in accordance with ASTM G-5. The reference potential for the experiments was supplied via a Saturated Calomel Electrode (S.C.E.). The corrosion resistances of the coatings were measured by weight loss after immersion of free standing coatings, which were prepared by chemically dissolving the aluminum substrate. The adhesive and abrasive wear rates of the coatings were measured in accordance with the ASTM standards D2714-68 and G-65, respectively.
RESULTS AND DISCUSSION The compositions of the alloys used in this study were chosen to Mat. Res.
Soc.
Symp.
Proc. Vol.
28 (1984)
QElsevier Science Publishing Co.,
Inc.
234
investigate the effect of molybdenum and chromiun contents on hardness and The compositions are listed in Table 1, along with corrosion res
Data Loading...
